M
Maggot debridement therapy
Magnesium
Magnetic therapy
Mares and IR/PPID
Medicines and drugs
Metalloproteinases- MMPs (matrix metalloproteinases), ADAM and ADAMTS proteins
Metformin
Microbiome
Minerals
MIRG
MRI
Muscle wasting
Muzzles
Maggot debridement therapy
Following laminitis infection of tissue and bone can develop in the feet due to dead tissue and blood vessel damage. Sterile fly maggots can be used to debride necrotic wound tissue and stimulate healing. Specially bred Medical Maggots are placed over the wound or infected tissue and kept in place with bandages, and consume dead and diseased tissue, leaving healthy tissue. Maggot debridement therapy may be used alongside regional limb perfusion.
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Maggot Debridement Therapy posted on Daisy Haven Farm: School of Integrative Hoofcare Facebook page February 2023
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Maggot Debridement Therapy used on a foot abscess, removed by soaking the foot with Cleantrax. Posted by Daisy Haven Farm 16 September 2023 on YouTube
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More maggot debridement therapy posted on Daisy Haven Farm: School of Integrative Hoofcare February 2023.
Daisy uses medical maggots to debride hoof infection, and is often able to avoid surgical debridement as a result. The maggots only eat dead (necrotic) tissue, and stimulate growth of new tissue.
Daisy uses medical maggots to debride hoof infection, and is often able to avoid surgical debridement as a result. The maggots only eat dead (necrotic) tissue, and stimulate growth of new tissue.
Biomonde - larval debridement therapy (UK/Europe)
Monarch Labs - medical grade maggots (USA)
How to apply MDT Dressings on Horses and Other Animals - Monarch Labs
Subsolar Abscess and Coffin Bone Osteomyelitis - ACVS
Freeman SL, Ashton NM, Elce YA, Hammond A, Hollis AR, Quinn G.
BEVA primary care clinical guidelines: Wound management in the horse.
Equine Vet J. 2021 Jan;53(1):18-29. doi: 10.1111/evj.13289. Epub 2020 Jul 17. PMID: 32463930.
The authors asked does the use of larvae debridement reduce the duration of healing/reduce the rate of infection.. of wound healing in horses compared to wounds that are not treated with larva debridement? Papers by Lepage et al. and Sherman et al. were consulted (see below). The authors suggest both papers were retrospective with very low quality evidence, but that a positive outcome was reported in selected cases where conventional methods of wound debridement had failed or were not practical, such as necrotic hoof defects.
What is that hole in the coffin bone? Diagnosis and Treatment of Septic Pedal Osteitis and Keratomas in the Horse - Ashleigh Olds-Sanchez 2019
"Medical Maggots - Clinical impressions:
Speed healing, Reduce patient pain
Two cases had surgical debridement for similar pedal osteitis cases. One owner allowed maggots, other didn’t. Horse treated with maggots left the hospital 30 days sooner than the horse not treated with maggots."
Choudhary V, Choudhary M, Pandey S, Chauhan VD, Hasnani JJ
Maggot debridement therapy as primary tool to treat chronic wound of animals
Vet World. 2016;9(4):403-409. doi:10.14202/vetworld.2016.403-409
"Clinical studies evaluated that MDT is more efficient and safe technique for chronic wounds as compared to conventional therapy. Maggots are supplied by licensed laboratories in sterile bottles, which make it very safe, efficient, and easy method of healing for chronic wounds and prevents secondary bacterial infections."
Got Maggots? Maggot Debridement Therapy Daisy Haven Farm Style - Daisy Bicking April 2015 EasyCare Inc
Easy application of Maggot Debridement Therapy to treat chronic abscesses in laminitic horses - Daisy Bicking
French Sterile Maggot Debridement Study Finds 93% Efficacy for Equine Wounds - The Hoof Blog, Fran Jurga, March 2013
Equine Veterinary Journal Volume 44, Issue Supplement S43, Article first published online: 27 NOV 2012
The use of maggot debridement therapy in 41 equids
Lepage OM, Doumbia A, Perron-Lepage MF, Gangl M
Introduction: Maggot debridement therapy (MDT) uses freshly emerged, germ-free larvae of the common green bottle fly. Wound healing is attributed to a debridement effect and production of potent proteolytic enzymes, antiseptic effect, direct effect on cytokine and cell proliferation, and breakdown of biofilm formation, and destruction and digestion of bacteria.
Maggots are applied to a wound either directly (loose "free range" maggots applied directly to the wound surface) or indirectly (maggots contained in a biobag).
MDT has been used in horses for septic navicular bursitis, complicated laminitis, pedal bone osteomyelitis and other hoof diseases, and supraspinous bursitis.
Methods: 41 horses and donkeys were treated with MDT in France or Mali.
The number of maggots to use was based on the size of the wound calculated approximately 5-10 maggots per cm2 of wound surface area x depth - 300 to 900 maggots per MDT were used. Maggots not used immediately were stored at 8-10'C.
Wounds were prepared with a light surgical debridement to remove debris and dry necrotic tissue and to allow for drainage from the lowest point of the wound. For foot wounds, hoof wall resection was performed to allow good access to the lesion and allow drainage. All local treatments and systemic antibiotics were stopped (except RLP using gentamicin). Non-permeable (occlusive) dressings/film should not be used. A nylon retention net or elastic cohesive bandage was applied to keep the maggots in the area of the wound. For foot wounds free range maggots or a biobag of maggots were applied to the surface of the wound, then covered with net, gauze sponge (absorbent cotton pads or nappy could also be applied), and non-occlusive bandage (or orthopaedic shoe with a plate) applied. Outer dressings were changed 1-3 x a day as necessary. The maggots were left in place for 72 hours, and if required replaced with fresh larvae (left in place for another 3-4 days). The maggots generally failed to survive or were not effective after 4 days.
Results: of the hoof infections described:
3 horses with septic navicular bursa had free range maggots applied plus RLP, 1 case required 2 applications of maggots, all healed.
1 horse with a keratoma had free range maggots applied following a hoof wall resection, healed.
3 horses with septic pedal bone osteitis had free range maggots applied following sole resection, 1 case required 2 applications of maggots, all healed.
A red-brown exudate was produced from the wounds after 12-24 hours (considered evidence of removal of necrotic tissue by the maggots), and some horses showed signs of discomfort (rubbing the wound, moving the treated limb) 24-36 hours after starting treatment.
Free range or biobag? The biobag manufacturers advise that tiny pieces of foam inside the net help to stimulate maggot activity and assist with exudate management; however better results from free range maggots compared to biobags were found in humans. The authors' treatment of choice for horses was direct contact with free range maggots, except where a very focal cavity or area was involved.
Discussion: In this study no more than 2 MDT treatments were required, and healthy granulation tissue was present after 3 days of treatment.
The authors conclude: "maggot debridement therapy can be recommended for debridement of wounds and its potent antibacterial effects, including the control of difficult infections such as MRSA or other multi-antibiotic resistant bacteria. Maggot debridement therapy can also be used to treat many types of lesions including complicated and deep lacerations, abscesses, abdominal wound dehiscence and infections even in the presence of internal fixation. However, maggot debridement therapy is not recommended for treatment of wounds occuring in association with neoplasia or if bone sequestration is suspected. Due to the actual cost associated with this form of therapy, maggot debridement therapy should be considered for lesions that fail to respond to conventional methods. Maggot debridement therapy potentially has an integral place in modern veterinary wound care but additional clinical studies are needed to assess its impact and value."
Morrison S.
Maggot debridement therapy for laminitis.
Vet Clin North Am Equine Pract. 2010 Aug;26(2):447-50. doi: 10.1016/j.cveq.2010.06.002. PMID: 20699186.
Bras RJ, Morrison S
Retrospective case series of 20 horses (2002-2009) sustaining puncture wounds to the navicular bursa with maggot debridement therapy as an adjunctive treatment
AAEP Proceedings 2009 Vol 55
"A non-traumatic method for removal of necrotic tissue and bacteria is beneficial for the most optimal outcome. Maggot debridement therapy is a nontraumatic, minimally invasive method to remove necrotic tissue from an extensive foot infection1 (Fig. 8). Maggot debridement therapy (MDT) is the medical use of specially selected disinfected green blow fly larvae (maggots) for cleaning non-healing wounds. Medicinal maggots have been found to have four principle actions: (1) debride wounds by dissolving the necrotic, infected tissue; (2) disinfect the wound by killing bacteria; (3) stimulate wound healing; and (4) break down and inhibit the formation of biofilm....Proteolytic enzymes seem to be responsible for the debriding or liquefying action of the maggots on the necrotic tissue, while the maggot-derived proteins do indeed kill bacteria and promote wound healing.2 Maggot therapy is believed to not only debride necrotic tissue, but also to stimulate fibroblast activity and angiogenesis. Larval therapy can be useful in debriding residual necrotic tissue after surgical debridement. This combination of treatment is an effective way to debride diseased tissue without disturbing the normal architecture of the foot. Regional limb perfusions and systemic antibiotics can be used along with maggot therapy and seem to have no harmful effects on the larvae within the wound."
Sherman RA, Morrison S, Ng D
Maggot debridement therapy for serious horse wounds - a survey of practitioners
Veterinary Journal (London, England : 1997). 2007 Jul;174(1):86-91. DOI: 10.1016/j.tvjl.2006.05.012
Morrison SE
How to use sterile maggot debridement therapy for foot infections of the horse.
Proceedings of the Annual Convention of the American Association Equine Practitioners. Seattle (WA): AAEP; 2005.
How To Use Sterile Maggot Debridement Therapy (AAEP Convention 2005) by Kimberly S. Brown
The Horse.com February 17 2006, Article # 6540
Magnesium
Does magnesium help with insulin dysregulation/EMS/weight loss?
Winter J C, Liertz S, Merle R, Aschenbach J R, Gehlen H
Oral supplementation of magnesium aspartate hydrochloride in horses with Equine Metabolic Syndrome
Pferdeheilkunde 2016 vol 32(4) p372-377. DOI: 10.21836/PEM20160410 (ResearchGate - full paper)
5 horses (mean age 14.2) with EMS, diagnosed from CGIT results, were fed 30 mg/kg BW magnesium as magnesium aspartate hydrochloride for 3 months. No adverse effects were seen. There were no significant changes in body weight, BCS (7-8/9 before and after treatment) and cresty neck score (3-4/5 before and after treatment). Serum magnesium concentrations were within the normal range before supplementation with magnesium, and there were slight but not significant changes in serum magnesium concentration after supplementation. There were no significant changes in ACTH, RISQI, MIRG, GGT and triglycerides. 3/5 horses had improved CGIT results.
TLS comment: How much magnesium was in the diet before supplementation? What was the diet? What time of year was the research carried out - during the seasonal rise (August to October) there may be a natural increase in insulin resistance. What were the baseline insulin and glucose concentrations - why are RISQI and MIRG given and not the baseline insulin and glucose results? No controls were used - improvements may have had nothing to do with supplementation - experiments should always be controlled! Note there were no improvements in body condition score or cresty neck score after 3 months of magnesium supplementation.
Dietary management of insulin resistance - Pat Harris - Waltham - 2013
Chameroy KA, Frank N, Elliott SB, Boston RC
Effects of a supplement containing chromium and magnesium on morphometric measurements, resting glucose, insulin concentrations and insulin sensitivity in laminitic obese horsesEquine Vet J. 2011 Jul;43(4):494-9 (PubMed)
Conclusions: "The supplement containing chromium and magnesium evaluated in this study did not alter morphometric measurements, blood variables, resting insulin concentrations or insulin sensitivity in laminitic obese horses."
The above paper is based on KellyAnn Chameroy's PhD dissertation - see chapter 2 p 59:
Diagnosis and Management of Horses with Equine Metabolic Syndrome (EMS)
Chameroy KA, PhD dissertation 2010
Stewart AJ
Magnesium disorders in horses
Vet Clin North Am Equine Pract. 2011 Apr;27(1):149-63 (PubMed)
"Magnesium (Mg) is an essential macroelement that is required for cellular energy-dependent reactions involving adenosine triphosphate and for the regulation of calcium channel function. Subclinical hypomagnesemia is common in critically ill humans and animals and increases the severity of the systemic inflammatory response syndrome; worsens the systemic response to endotoxins; and can lead to ileus, cardiac arrhythmias, refractory hypokalemia, and hypocalcemia. This article discusses the clinical signs, consequences, and treatment of hypomagnesemia in horses and describes the association of Mg and endotoxemia, insulin resistance, and brain injury."
This in-depth article on magnesium deficiency in horses suggests that whole body chronic magnesium deficiency is rare in horses, and that supplementation is unlikely to be necessary when a horse is fed a normal diet. However, supplementation with magnesium is unlikely to harm a horse with healthy kidney function. There are anecdotal reports that supplementing magnesium can help reduce cresty necks and the incidence of laminitis, but currently there is no published research to support this.
Magnesium - research in humans
Equine Applied and Clinical Nutrition refers to this research:
Diabet Med. 2006 Oct;23(10):1050-6 (PubMed)
Effects of oral magnesium supplementation on glycaemic control in Type 2 diabetes: a meta-analysis of randomized double-blind controlled trials
Song Y, He K, Levitan EB, Manson JE, Liu S
which concluded: "oral magnesium supplementation for 4-16 weeks may be effective in reducing plasma fasting glucose levels and raising HDL cholesterol in patients with Type 2 diabetes, although the long-term benefits and safety of magnesium treatment on glycaemic control remain to be determined", but only in people who were deficient in magnesium before supplementation.
More recent research found that most adults with metabolic syndrome failed to reach the recommended daily magnesium intake, and that "meeting the RDA for magnesium may demonstrate a protective effect on insulin resistance":
Nutrients. 2013 Sep 27;5(10):3910-9 (PubMed) (Full paper)
Dietary magnesium intake improves insulin resistance among non-diabetic individuals with metabolic syndrome participating in a dietary trial
Wang J, Persuitte G, Olendzki BC, Wedick NM, Zhang Z, Merriam PA, Fang H, Carmody J, Olendzki GF, Ma Y
Does magnesium help with insulin dysregulation/EMS/weight loss?
Winter J C, Liertz S, Merle R, Aschenbach J R, Gehlen H
Oral supplementation of magnesium aspartate hydrochloride in horses with Equine Metabolic Syndrome
Pferdeheilkunde 2016 vol 32(4) p372-377. DOI: 10.21836/PEM20160410 (ResearchGate - full paper)
5 horses (mean age 14.2) with EMS, diagnosed from CGIT results, were fed 30 mg/kg BW magnesium as magnesium aspartate hydrochloride for 3 months. No adverse effects were seen. There were no significant changes in body weight, BCS (7-8/9 before and after treatment) and cresty neck score (3-4/5 before and after treatment). Serum magnesium concentrations were within the normal range before supplementation with magnesium, and there were slight but not significant changes in serum magnesium concentration after supplementation. There were no significant changes in ACTH, RISQI, MIRG, GGT and triglycerides. 3/5 horses had improved CGIT results.
TLS comment: How much magnesium was in the diet before supplementation? What was the diet? What time of year was the research carried out - during the seasonal rise (August to October) there may be a natural increase in insulin resistance. What were the baseline insulin and glucose concentrations - why are RISQI and MIRG given and not the baseline insulin and glucose results? No controls were used - improvements may have had nothing to do with supplementation - experiments should always be controlled! Note there were no improvements in body condition score or cresty neck score after 3 months of magnesium supplementation.
Dietary management of insulin resistance - Pat Harris - Waltham - 2013
Chameroy KA, Frank N, Elliott SB, Boston RC
Effects of a supplement containing chromium and magnesium on morphometric measurements, resting glucose, insulin concentrations and insulin sensitivity in laminitic obese horsesEquine Vet J. 2011 Jul;43(4):494-9 (PubMed)
Conclusions: "The supplement containing chromium and magnesium evaluated in this study did not alter morphometric measurements, blood variables, resting insulin concentrations or insulin sensitivity in laminitic obese horses."
The above paper is based on KellyAnn Chameroy's PhD dissertation - see chapter 2 p 59:
Diagnosis and Management of Horses with Equine Metabolic Syndrome (EMS)
Chameroy KA, PhD dissertation 2010
Stewart AJ
Magnesium disorders in horses
Vet Clin North Am Equine Pract. 2011 Apr;27(1):149-63 (PubMed)
"Magnesium (Mg) is an essential macroelement that is required for cellular energy-dependent reactions involving adenosine triphosphate and for the regulation of calcium channel function. Subclinical hypomagnesemia is common in critically ill humans and animals and increases the severity of the systemic inflammatory response syndrome; worsens the systemic response to endotoxins; and can lead to ileus, cardiac arrhythmias, refractory hypokalemia, and hypocalcemia. This article discusses the clinical signs, consequences, and treatment of hypomagnesemia in horses and describes the association of Mg and endotoxemia, insulin resistance, and brain injury."
This in-depth article on magnesium deficiency in horses suggests that whole body chronic magnesium deficiency is rare in horses, and that supplementation is unlikely to be necessary when a horse is fed a normal diet. However, supplementation with magnesium is unlikely to harm a horse with healthy kidney function. There are anecdotal reports that supplementing magnesium can help reduce cresty necks and the incidence of laminitis, but currently there is no published research to support this.
Magnesium - research in humans
Equine Applied and Clinical Nutrition refers to this research:
Diabet Med. 2006 Oct;23(10):1050-6 (PubMed)
Effects of oral magnesium supplementation on glycaemic control in Type 2 diabetes: a meta-analysis of randomized double-blind controlled trials
Song Y, He K, Levitan EB, Manson JE, Liu S
which concluded: "oral magnesium supplementation for 4-16 weeks may be effective in reducing plasma fasting glucose levels and raising HDL cholesterol in patients with Type 2 diabetes, although the long-term benefits and safety of magnesium treatment on glycaemic control remain to be determined", but only in people who were deficient in magnesium before supplementation.
More recent research found that most adults with metabolic syndrome failed to reach the recommended daily magnesium intake, and that "meeting the RDA for magnesium may demonstrate a protective effect on insulin resistance":
Nutrients. 2013 Sep 27;5(10):3910-9 (PubMed) (Full paper)
Dietary magnesium intake improves insulin resistance among non-diabetic individuals with metabolic syndrome participating in a dietary trial
Wang J, Persuitte G, Olendzki BC, Wedick NM, Zhang Z, Merriam PA, Fang H, Carmody J, Olendzki GF, Ma Y
Magnetic therapy
Could magnetic therapy help horses with laminitis?
Any claims made by companies selling magnetic therapy products should be backed by peer-reviewed published research. TLS has yet to find any research supporting the efficacy of magnetic therapy for horses or humans.
Equine magnetic therapy: the positives and negatives - K Marcella, Jan 2009, DVM360 Magazine
Research that did not find a benefit from using magnetic therapy:
J Am Vet Med Assoc. 2000 Sep 15;217(6):874-7 (Full)
Effect of a static magnetic field on blood flow to the metacarpus in horses
Steyn PF, Ramey DW, Kirschvink J, Uhrig J
"Results suggest that in horses, the static magnetic field associated with application of commercially available magnetic wraps for 48 hours does not increase blood flow to the portion of the metacarpus underneath the wrap."
CMAJ. 2007 Sep 25;177(7):736-42 (Full)
Static magnets for reducing pain: systematic review and meta-analysis of randomized trials
Pittler MH, Brown EM, Ernst E
Randomized trials of static magnets for treating pain were analysed, and concluded: "the meta-analysis suggested no significant effects of static magnets for pain relief relative to placebo." "The evidence does not support the use of static magnets for pain relief, and therefore magnets cannot be recommended as an effective treatment."
Research that did find a benefit from using magnetic therapy:
Arch Phys Med Rehabil. 1997 Nov;78(11):1200-3
Response of pain to static magnetic fields in postpolio patients: a double-blind pilot study
Vallbona C, Hazlewood CF, Jurida G
"The application of a device delivering static magnetic fields of 300 to 500 Gauss over a pain trigger point results in significant and prompt relief of pain in postpolio subjects."
For comment on this research, see Magnetic Therapy: Plausible Attraction? - James Livingston, Skeptical Inquirer Vol 22,4 July/Aug 1998
Comments on magnetic therapy:
Magnet Therapy: A Skeptical View - Stephen Barrett, Quackwatch, 2008
Magnet Therapy: A Billion-dollar Boondoggle - Bruce Flamm, Skeptical Inquirer Vol 30.4 July/August 2006
Could magnetic therapy help horses with laminitis?
Any claims made by companies selling magnetic therapy products should be backed by peer-reviewed published research. TLS has yet to find any research supporting the efficacy of magnetic therapy for horses or humans.
Equine magnetic therapy: the positives and negatives - K Marcella, Jan 2009, DVM360 Magazine
Research that did not find a benefit from using magnetic therapy:
J Am Vet Med Assoc. 2000 Sep 15;217(6):874-7 (Full)
Effect of a static magnetic field on blood flow to the metacarpus in horses
Steyn PF, Ramey DW, Kirschvink J, Uhrig J
"Results suggest that in horses, the static magnetic field associated with application of commercially available magnetic wraps for 48 hours does not increase blood flow to the portion of the metacarpus underneath the wrap."
CMAJ. 2007 Sep 25;177(7):736-42 (Full)
Static magnets for reducing pain: systematic review and meta-analysis of randomized trials
Pittler MH, Brown EM, Ernst E
Randomized trials of static magnets for treating pain were analysed, and concluded: "the meta-analysis suggested no significant effects of static magnets for pain relief relative to placebo." "The evidence does not support the use of static magnets for pain relief, and therefore magnets cannot be recommended as an effective treatment."
Research that did find a benefit from using magnetic therapy:
Arch Phys Med Rehabil. 1997 Nov;78(11):1200-3
Response of pain to static magnetic fields in postpolio patients: a double-blind pilot study
Vallbona C, Hazlewood CF, Jurida G
"The application of a device delivering static magnetic fields of 300 to 500 Gauss over a pain trigger point results in significant and prompt relief of pain in postpolio subjects."
For comment on this research, see Magnetic Therapy: Plausible Attraction? - James Livingston, Skeptical Inquirer Vol 22,4 July/Aug 1998
Comments on magnetic therapy:
Magnet Therapy: A Skeptical View - Stephen Barrett, Quackwatch, 2008
Magnet Therapy: A Billion-dollar Boondoggle - Bruce Flamm, Skeptical Inquirer Vol 30.4 July/August 2006
Mares and IR/PPID
Pregnancy
PPID
Seasons
Insulin
PCOS
Other research
Pregnancy
Insulin resistance is a normal occurrence in healthy pregnant mares, enabling the mother's nutrients to be redirected to the foal growing inside her. However, insulin resistance may be exacerbated in mares that had insulin dysregulation before becoming pregnant.
Disturbances in glucose and insulin metabolism during pregnancy can predispose the foal to metabolic disorders associated with insulin resistance later in life.
Foals from mares fed a high energy diet had lower basal insulin concentrations than foals from mares fed a low energy diet at 2 weeks, prior to weaning and at 10 months:
Hicks GR, Fraser NS, Bertin FR.
Changes Associated with the Peri-Ovulatory Period, Age and Pregnancy in ACTH, Cortisol, Glucose and Insulin Concentrations in Mares.
Animals (Basel). 2021 Mar 20;11(3):891. doi: 10.3390/ani11030891. PMID: 33804751; PMCID: PMC8003915. Open Access.
"ACTH concentrations change during a mare’s peri-ovulatory period and early pregnancy. Therefore, in addition to the seasonal diagnostic cut-off values, the interpretation of an immunoreactive plasma ACTH concentration should take into account the clinical context of a horse, including its reproductive status."
M. Robles, E. Nouveau, C. Gautier, L. Mendoza, C. Dubois, M. Dahirel, B. Lagofun, M-C Aubrière, J-P Lejeune, I. Caudron, I. Guenon, C. Viguié, L. Wimel, H. Bouraima-Lelong, D. Serteyn, A. Couturier-Tarrade, P. Chavatte-Palmer
Maternal obesity increases insulin resistance, low-grade inflammation and osteochondrosis lesions in foals and yearlings until 18 months of age
PLOS Published: January 26, 2018 https://doi.org/10.1371/journal.pone.0190309
Obese pregnant mares were more insulin resistant (according to FSIGT) than non-obese pregnant mares at 300 days. However, non-obese pregnant mares were mostly defined as insulin-sensitive by the FSIGT.
Beythien E, Wulf M, Ille N, Aurich J, Aurich C.
Effects of sex, pregnancy and season on insulin secretion and carbohydrate metabolism in horses.
Anim Reprod Sci. 2017 Sep;184:86-93. doi: 10.1016/j.anireprosci.2017.07.002. Epub 2017 Jul 6. PMID: 28701287.
Keywords: glucose, horse, insulin, pregnancy.
Oral glucose tests were performed on 12 pregnant mares and 10 geldings in June, September, December and March (geldings) or day 320 of gestation (mares). Plasma glucose concentrations increased after glucose was fed, with a greater increase in pregnant mares than geldings, and increased in mares with month of gestation, indicating reduced clearance and therefore a partial insulin resistance induced by pregnancy independent from season. The insulin response to glucose feeding and the relative insulin release increased from June to December indicating a seasonal change in beta-cell sensitivity [however, the abstract does not give details of other possible changes e.g. diet, bodyweight etc that might influence insulin].
Peugnet P, Robles M, Mendoza L, Wimel L, Dubois C, Dahirel M, Guillaume D, Camous S, Berthelot V, Toquet MP, Richard E, Sandersen C, Chaffaux S, Lejeune JP, Tarrade A, Serteyn D, Chavatte-Palmer P
Effects of moderate amounts of barley in late pregnancy on growth, glucose metabolism and osteoarticular status of pre-weaning horses
PLoS One. 2015 Apr 13;10(4):e0122596. doi: 10.1371/journal.pone.0122596
Galantino-Homer HL, Engiles JB
Insulin resistance and laminitis in broodmares
JEVS October 2013 Volume 33, Issue 10, Pages 844-846
"The endocrine change associated with pregnancy can increase the risk for laminitis in mares. All broodmares should be monitored and managed for laminitis and endocrine disorders."
Obesity and insulin resistance have several negative effects on fertility in mares. Mares that are insulin resistant or have uncorrected chronic laminitis prior to becoming pregnant may be at higher risk of laminitis. However, changes to insulin and glucose in late pregnancy and during lactation may be protective for some laminitic mares.
Galantino-Homer HL, Engiles JB
Insulin resistance and laminitis in broodmares
JEVS October 2012 Volume 32, Issue 10, Pages 680-688
Dobbs et al., Proc. Australasian Equine Sc. Symp. Vol 4, 2012 (p56)
Glucose and insulin dynamics in mares and their foals
Anderson et al., Proc. Australasian Equine Sc. Symp. Vol 4, 2012 (page 36)
Mares of lower body condition score exhibit marked insulin resistance and reduced insulin secretion in late gestation
Am J Vet Res. 2011 May;72(5):666-74. doi: 10.2460/ajvr.72.5.666
Evaluation of the effects of pregnancy on insulin sensitivity, insulin secretion and glucose dynamics in Thoroughbred mares
George LA, Staniar WB, Cubitt TA, Treiber KH, Harris PA, Geor RJ
"Pregnant mares had slower glucose clearance and greater insulin secretion at 28 weeks of gestation than did nonpregnant mares. Glucose and insulin responses to meal feeding, particularly with HS feed, were greater in pregnant mares, indicating that pregnancy enhanced the postprandial glycemic and insulinemic effects of starch-rich feed supplements."
Fowden AL, Comline RS, Silver M
Insulin secretion and carbohydrate metabolism during pregnancy in the mare
Equine Vet J. 1984 Jul;16(4):239-46
Pregnant mares (<270 days) had a mean insulin concentration of 130.5 uIU/ml after a grain meal compared to 62.4 uIU/ml.
Pregnant mares (<270 days) had a mean insulin concentration of 61.6 uIU/ml before feeding compared to 24.0 uIU/ml (source: McIntosh PhD 2006).
PPID
In humans ACTH has shown significant increases during pregnancy, and Andy Durham said that it is suspected that ACTH increases with pregnancy although we are not aware of a study into this (personal correspondence 2018). It may be best to base PPID diagnosis on clinical signs rather than ACTH testing during pregnancy.
Mares with PPID may fail to conceive or have abnormal heat cycles. Persistent lactation may also be linked to PPID. Reduced levels of dopamine affecting reproductive hormones, and chronic infections of the uterus have been suggested as contributing to infertility in mares with PPID, and pergolide treatment may restore fertility and normal seasons. (McFarlane 2011).
In her presentation "Is it PPID or is it EMS?" Dianne McFarlane suggested that infertility in breeding horses may be an early sign of PPID.
Pituitary Pars Intermedia Dysfunction: Challenges of Diagnosis and Treatment
Harold C. Schott II 2006 Vol. 52 AAEP proceedings
Clinical signs reported in horses with PPID include "persistent lactation and infertility, which are probably a consequence of altered release of prolactin and gonadotrophic hormones."
www.ecirhorse.org - physiology of PPID - PPID mares that had enlarged mammary glands and/or were leaking milk were found to have elevated blood prolactin concentrations.
Can pergolide be given to pregnant/lactating mares?
From www.prascend.com
"Question 5: Can PRASCEND be used in breeding, pregnant, or lactating mares?
Answer: PRASCEND has not been evaluated in breeding, pregnant, or lactating horses. As PRASCEND is a dopamine agonist, it may interfere with reproductive hormones involved in horses. Use only after a risk/benefit assessment by the attending veterinarian."
From the NOAH datasheet for Prascend under Contra-indications, warnings etc:
"Pregnancy: Use only according to the benefit/ risk assessment by the responsible veterinarian. The safety of this product has not been demonstrated in pregnant mares. Laboratory studies in mice and rabbits have not produced any evidence of teratogenic effects. Reduced fertility was seen in mice at a dose of 5.6 mg/kg body weight per day.
Lactation: The use is not recommended in lactating horses, in which the safety of this product has not been demonstrated. In mice, reduced body weights and survival rates in the progeny were attributed to the pharmacological inhibition of prolactin secretion resulting in lactation failure."
Dianne McFarlane (Equine Pituitary Pars Intermedia Dysfunction Vet. Clin. Equine 27 (2011) 93-113) says that giving pergolide to pregnant mares doesn't seem to cause adverse effects, but it is best discontinued a month before foaling.
Andy Durham and Cathy McGowan were asked about the use of pergolide for pregnant mares in the Boehringer Ingelheim webinar on 04 September 2012. Experience tends to be limited because PPID cases are generally older and often difficult to get in foal. Pregnant mares have been treated with pergolide, but because pergolide could suppress prolactin and therefore milk production, pergolide is often reduced or stopped before lactation. More...
Seasons
There are anecdotal reports that the spring transition may affect mares with PPID (see ECIR Group messages 164441, 154749) and see "insulin" below.
However, in published research there seems to be no evidence that there is any increase in ACTH in the spring:
Effects of pituitary pars intermedia dysfunction (PPID), season, and pasture diet on blood adrenocorticotropic hormone and metabolite concentrations in horses.
Sarah Beth Elliott Masters thesis 2010
See p38 - ACTH concentrations were at their lowest in spring months in both normal and PPID horses (geldings and mares).
See also p56.
Investigating PPID - Liphook Equine Hospital - see graph showing median and IQR ACTH concentrations by month for normal and PPID horses.
Equine Seasonal Cyclicity - Bruce E Eilts - www.vetmed.lsu.edu 2010
Repeatability of prolactin responses to sulpiride in mares and geldings and the effect of pergolide and cabergoline
Rebekah C. Hebert MSc thesis May 2012
"the increasing prolactin concentrations in the spring are involved with loss of the winter hair coat (Thompson et al., 1997) as well as the return of ovarian activity in mares (Nequin et al., 1993)".
Estradiol interactions with dopamine antagonists in mares: prolactin secretion and reproductive traits
Kristian Kandis Kelley MSc Thesis May 2006
"Thompson et al. (1986) reported that horses have higher prolactin levels during the breeding season, with mares having the highest levels. Mares undergoing transition from the anovulatory season in winter to the breeding season experience increases in several hormones, including prolactin."
Insulin
Eleanor M Kellon
Reproductive abnormalities in mares with diet-resistant insulin resistance
No Laminitis Conference Sept 2013 (IVIS)
The ECIR group has had reports of udder enlargement, lactation, irregular cycling and cycles affecting hoof comfort in mares. Several mares with severe insulin resistance that hasn't responded to normal diet restrictions have shown symptoms similar to PCOS in women. There is little evidence that mares have the higher androgen levels found in women with PCOS. Other than around ovulation, FSH levels should be higher than LH in mares, and finding normal to high LH with normal to low FHS can be suggestive. Treatment with estrogens may reduce insulin resistance and laminitis in these mares.
Owners who suspect their mares are affected should join the ECIR Group and/or contact Dr Kellon.
The Impact of Insulin on the Matrix Metalloproteinase System during Equine Follicular Development and Atresia
D R Sessions PhD dissertation 2008
Reprod Fertil Dev 2006;18(6):609-17. (PubMed)
Obesity is associated with altered metabolic and reproductive activity in the mare: effects of metformin on insulin sensitivity and reproductive cyclicity.
Vick M, Sessions D, Murphy B, Kennedy E, Reedy S, Fitzgerald B
"obese mares exhibited a significantly longer duration of the oestrous cycle, significant increases in circulating concentrations of leptin and insulin, and decreased insulin sensitivity and concentrations of thyroxine compared with feed-restricted mares throughout the experiment."
DR Sessions, SE Reedy, MM Vick, BA Murphy, BP Fitzgerald
Development of a model for inducing transient insulin resistance in the mare: Preliminary implications regarding the estrous cycle
J ANIM SCI 2004, 82:2321-2328
(PubMed) Abstract: Peripheral insulin resistance is the failure of proper cellular glucose uptake in response to insulin. Insulin resistance and hyperinsulinemia are associated with several disease states in the horse and reproductive function disturbances in humans, including polycystic ovarian syndrome. To test the hypothesis that insulin resistance (IR) and hyperinsulinemia disrupt the estrous cycle in mares, two experiments were conducted to first develop a model to induce IR and to then examine the effect of this model on the duration of the estrous cycle. In Exp. 1, a hyperinsulinemic-euglycemic clamp (HEC) procedure was performed on seven mares to determine insulin sensitivity before and immediately following infusion of a heparinized lipid solution. The HEC procedure was repeated 1 wk after lipid infusion. Mares developed IR following the lipid infusion (P < 0.05), and some individuals maintained IR for up to 1 wk. Mares also exhibited increased blood insulin both immediately following treatment and 1 wk later (P < 0.05). In Exp. 2, induction of insulin resistance by lipid solution was not accompanied by changes in circulating concentrations of luteinizing hormone, and duration of the luteal phase, compared with the duration of untreated luteal phases. Nonetheless, lipid infusion and the resultant insulin resistance were associated with an increased interovulatory period (P < 0.05), and peak concentrations of progesterone (P < 0.05) were higher during the treated vs. untreated luteal phases of the estrous cycle. The results from the preliminary study suggest that infusion of a lipid solution may induce transient insulin resistance and hyperinsulinemia. The resulting insulin resistance and hyperinsulinemia may modify characteristics of the estrous cycle, perhaps at the level of the ovary.
PCOS Polycystic ovarian syndrome
Morresey P
Metabolic Syndrome in the Pregnant Mare
AAEP Proceedings 2012 Vol 58
In human women, polycystic ovary syndrome (PCOS) is considered a prediabetic state with clinical signs including insulin resistance, obesity and dyslipidemia, and is associated with the development of gestational diabetes. In women, metformin is often prescribed for PCOS and gestational diabetes. "Usage during pregnancy has been shown to improve insulin resistance in hyperinsulinemic PCOS women, with the most benefit seen in those with the greatest insulin resistance and endocrinopathy before conception" (see Glueck et al. 2004 Metformin during pregnancy reduces insulin, insulin resistance, insulin secretion, weight, testosterone and development of gestational diabetes). "Insulin has a major role in the regulation of ovarian steroidogenesis, follicular development, and granulosa cell proliferation. The insulin-like growth factor system is therefore affected, and, as this has been shown crucial to follicle selection and dominance in the mare, disturbances of ovarian function may be seen. Obese mares with reduced insulin sensitivity have been shown to have prolonged interovulatory and luteal phases. A parallel between PCOS in women and disturbances of follicular dynamics in mares can therefore be drawn."
See also Do Equine Metabolic Diseases Affect Reproduction? Erica Larson September 2013 thehorse.com
Munzner, Eyra
Do obese ponies suffer from an equine version of polycystic ovarian syndrome (PCOS)?
Thesis 2010 Charles Sturt University
"Polycystic ovarian syndrome (PCOS) is a highly prevalent and debilitating disease which can have serious consequences for women of reproductive age, including infertility, increased risk of cardiovascular disease and the need for lifelong drug therapy. Further research into the cause and treatment of PCOS has been hampered by the lack of a suitable animal model. It has been identified that pony mares exhibit many of the signs and symptons of PCOS, including obesity, insulin resistance and potential breeding difficulties, and therefore this study aims to, firstly, identify whether pony mares suffer from a condition similar to PCOS, and, secondly, to determine the suitability of pony mares as an animal model for further research into PCOS...."
Other research
Cadario M, Archbald L
Effect of endocrinopathies on fertility in the mare. Part 1: Equine metabolic syndrome
Theriogenology Annual Conference July 2022 published September 2022
Cadario M, Archbald L
Effect of endocrinopathies on fertility in the mare. Part 2: Pituitary pars intermedia dysfunction
Theriogenology Annual Conference July 2022 published September 2022
Ousey JC, Fowden AL, Wilsher S, Allen WR
The effects of maternal health and body condition on the endocrine responses of neonatal foals
Equine Vet J. 2008 Nov;40(7):673-9. doi: 10.2746/042516408x322175. PMID: 19165937
5 first time pregnant mares received a diet to maintain moderate body condition score, and 5 received a diet to maintain a high body condition score. All mares became ill mid-pregnancy and lost around 10% of their weight. During and for one month following their illness/weight loss, insulin and glucose concentrations decreased. Most parameters recorded were similar between foals after birth, but insulin concentrations during glucose tolerance tests were significantly higher in foals from moderate BCS diet mares, when compared to foals from high BCS diet mares. Conclusion: "Acute nutrient restriction in mid gestation caused by maternal illness and inappetence, superimposed on a maintenance feed intake throughout pregnancy, enhanced insulin secretion to glucose in foals." Potential relevance: "Disturbances in neonatal pancreatic beta cell function programmed during pregnancy may predispose foals to metabolic problems in later life."
Hedberg Y, Dalin AM, Forsberg M, Lundeheim N, Hoffmann B, Ludwig C, Kindahl H
Effect of ACTH (tetracosactide) on steroid hormone levels in the mare. Part A: effect in intact normal mares and mares with possible estrous related behavioral abnormalities
Anim Reprod Sci. 2007 Jul;100(1-2):73-91. Epub 2006 Jul 25
Ovariectomized mares and mares with inactive ovaries may show signs of estrus, possibly due to adrenal steroid hormones. Aberrant adrenal hormone production has been suggested as the cause for behavioural changes in some mares. Normal (N) mares and "problem" mares with "deviant estrous bevaviour (P) were given exogenous ACTH or saline. ACTH caused a significant increase in plasma levels of cortisol, progesterone, androstenedione and testosterone in all mares. Problem mares had a lower increase in cortisol and higher increase in progesterone. "The reason for the reduced adreno-cortical reactivity, with a low cortisol response to the ACTH treatment, in the 'problem' mares is unknown, but may indicate a difference in adrenal function as compared to control mares."
Hedberg Y, Dalin AM, Forsberg M, Lundeheim N, Sandh G, Hoffmann B, Ludwig C, Kindahl H
Effect of ACTH (tetracosactide) on steroid hormone levels in the mare. Part B: effect in ovariectomized mares (including estrous behavior)
Anim Reprod Sci. 2007 Jul;100(1-2):92-106
Mares may display estrous signs after ovariectomy. Exogenous ACTH increased cortisol, progesterone, androstenedione and testosterone in normal (N) and ovariectomized (O) mares. Cortisol levels were not different between N and O mares. Androstenedione, progesterone and testosterone levels were lower and increased less after ACTH in O mares.
" It was concluded that ovariectomy affected basal cortisol pattern. Ovarian androstenedione and testosterone contributed to the basal circulating levels and, in the case of androstenedione, was stimulated by ACTH. Endogenous estradiol did not act stimulatory on adrenal gland hormone production in the mare."
Asa CS, Goldfoot DA, Garcia MC, Ginther OJ
Dexamethasone suppression of sexual behavior in the ovariectomized mare
Hormones and Behavior Volume 14, Issue 1, March 1980, Pages 55–64
"estrous behavior seen in ovariectomized mares may be due to steroids from the adrenal cortex" ... "other adrenal steroids, e.g., androgens, may be involved in estrous behavior in the untreated, ovariectomized mare".
P M McCue
Review of ovarian abnormalities in the mare
AAEP Proceedings Vol 44 1998
Fowden AL, Comline RS, Silver M
Insulin secretion and carbohydrate metabolism during pregnancy in the mare
Equine Vet J. 1984 Jul;16(4):239-46. doi: 10.1111/j.2042-3306.1984.tb01919.x. PMID: 6383807 (Full paper: Deepdyve)
PPID
Seasons
Insulin
PCOS
Other research
Pregnancy
Insulin resistance is a normal occurrence in healthy pregnant mares, enabling the mother's nutrients to be redirected to the foal growing inside her. However, insulin resistance may be exacerbated in mares that had insulin dysregulation before becoming pregnant.
Disturbances in glucose and insulin metabolism during pregnancy can predispose the foal to metabolic disorders associated with insulin resistance later in life.
Foals from mares fed a high energy diet had lower basal insulin concentrations than foals from mares fed a low energy diet at 2 weeks, prior to weaning and at 10 months:
Hicks GR, Fraser NS, Bertin FR.
Changes Associated with the Peri-Ovulatory Period, Age and Pregnancy in ACTH, Cortisol, Glucose and Insulin Concentrations in Mares.
Animals (Basel). 2021 Mar 20;11(3):891. doi: 10.3390/ani11030891. PMID: 33804751; PMCID: PMC8003915. Open Access.
"ACTH concentrations change during a mare’s peri-ovulatory period and early pregnancy. Therefore, in addition to the seasonal diagnostic cut-off values, the interpretation of an immunoreactive plasma ACTH concentration should take into account the clinical context of a horse, including its reproductive status."
M. Robles, E. Nouveau, C. Gautier, L. Mendoza, C. Dubois, M. Dahirel, B. Lagofun, M-C Aubrière, J-P Lejeune, I. Caudron, I. Guenon, C. Viguié, L. Wimel, H. Bouraima-Lelong, D. Serteyn, A. Couturier-Tarrade, P. Chavatte-Palmer
Maternal obesity increases insulin resistance, low-grade inflammation and osteochondrosis lesions in foals and yearlings until 18 months of age
PLOS Published: January 26, 2018 https://doi.org/10.1371/journal.pone.0190309
Obese pregnant mares were more insulin resistant (according to FSIGT) than non-obese pregnant mares at 300 days. However, non-obese pregnant mares were mostly defined as insulin-sensitive by the FSIGT.
Beythien E, Wulf M, Ille N, Aurich J, Aurich C.
Effects of sex, pregnancy and season on insulin secretion and carbohydrate metabolism in horses.
Anim Reprod Sci. 2017 Sep;184:86-93. doi: 10.1016/j.anireprosci.2017.07.002. Epub 2017 Jul 6. PMID: 28701287.
Keywords: glucose, horse, insulin, pregnancy.
Oral glucose tests were performed on 12 pregnant mares and 10 geldings in June, September, December and March (geldings) or day 320 of gestation (mares). Plasma glucose concentrations increased after glucose was fed, with a greater increase in pregnant mares than geldings, and increased in mares with month of gestation, indicating reduced clearance and therefore a partial insulin resistance induced by pregnancy independent from season. The insulin response to glucose feeding and the relative insulin release increased from June to December indicating a seasonal change in beta-cell sensitivity [however, the abstract does not give details of other possible changes e.g. diet, bodyweight etc that might influence insulin].
Peugnet P, Robles M, Mendoza L, Wimel L, Dubois C, Dahirel M, Guillaume D, Camous S, Berthelot V, Toquet MP, Richard E, Sandersen C, Chaffaux S, Lejeune JP, Tarrade A, Serteyn D, Chavatte-Palmer P
Effects of moderate amounts of barley in late pregnancy on growth, glucose metabolism and osteoarticular status of pre-weaning horses
PLoS One. 2015 Apr 13;10(4):e0122596. doi: 10.1371/journal.pone.0122596
Galantino-Homer HL, Engiles JB
Insulin resistance and laminitis in broodmares
JEVS October 2013 Volume 33, Issue 10, Pages 844-846
"The endocrine change associated with pregnancy can increase the risk for laminitis in mares. All broodmares should be monitored and managed for laminitis and endocrine disorders."
Obesity and insulin resistance have several negative effects on fertility in mares. Mares that are insulin resistant or have uncorrected chronic laminitis prior to becoming pregnant may be at higher risk of laminitis. However, changes to insulin and glucose in late pregnancy and during lactation may be protective for some laminitic mares.
Galantino-Homer HL, Engiles JB
Insulin resistance and laminitis in broodmares
JEVS October 2012 Volume 32, Issue 10, Pages 680-688
Dobbs et al., Proc. Australasian Equine Sc. Symp. Vol 4, 2012 (p56)
Glucose and insulin dynamics in mares and their foals
Anderson et al., Proc. Australasian Equine Sc. Symp. Vol 4, 2012 (page 36)
Mares of lower body condition score exhibit marked insulin resistance and reduced insulin secretion in late gestation
Am J Vet Res. 2011 May;72(5):666-74. doi: 10.2460/ajvr.72.5.666
Evaluation of the effects of pregnancy on insulin sensitivity, insulin secretion and glucose dynamics in Thoroughbred mares
George LA, Staniar WB, Cubitt TA, Treiber KH, Harris PA, Geor RJ
"Pregnant mares had slower glucose clearance and greater insulin secretion at 28 weeks of gestation than did nonpregnant mares. Glucose and insulin responses to meal feeding, particularly with HS feed, were greater in pregnant mares, indicating that pregnancy enhanced the postprandial glycemic and insulinemic effects of starch-rich feed supplements."
Fowden AL, Comline RS, Silver M
Insulin secretion and carbohydrate metabolism during pregnancy in the mare
Equine Vet J. 1984 Jul;16(4):239-46
Pregnant mares (<270 days) had a mean insulin concentration of 130.5 uIU/ml after a grain meal compared to 62.4 uIU/ml.
Pregnant mares (<270 days) had a mean insulin concentration of 61.6 uIU/ml before feeding compared to 24.0 uIU/ml (source: McIntosh PhD 2006).
PPID
In humans ACTH has shown significant increases during pregnancy, and Andy Durham said that it is suspected that ACTH increases with pregnancy although we are not aware of a study into this (personal correspondence 2018). It may be best to base PPID diagnosis on clinical signs rather than ACTH testing during pregnancy.
Mares with PPID may fail to conceive or have abnormal heat cycles. Persistent lactation may also be linked to PPID. Reduced levels of dopamine affecting reproductive hormones, and chronic infections of the uterus have been suggested as contributing to infertility in mares with PPID, and pergolide treatment may restore fertility and normal seasons. (McFarlane 2011).
In her presentation "Is it PPID or is it EMS?" Dianne McFarlane suggested that infertility in breeding horses may be an early sign of PPID.
Pituitary Pars Intermedia Dysfunction: Challenges of Diagnosis and Treatment
Harold C. Schott II 2006 Vol. 52 AAEP proceedings
Clinical signs reported in horses with PPID include "persistent lactation and infertility, which are probably a consequence of altered release of prolactin and gonadotrophic hormones."
www.ecirhorse.org - physiology of PPID - PPID mares that had enlarged mammary glands and/or were leaking milk were found to have elevated blood prolactin concentrations.
Can pergolide be given to pregnant/lactating mares?
From www.prascend.com
"Question 5: Can PRASCEND be used in breeding, pregnant, or lactating mares?
Answer: PRASCEND has not been evaluated in breeding, pregnant, or lactating horses. As PRASCEND is a dopamine agonist, it may interfere with reproductive hormones involved in horses. Use only after a risk/benefit assessment by the attending veterinarian."
From the NOAH datasheet for Prascend under Contra-indications, warnings etc:
"Pregnancy: Use only according to the benefit/ risk assessment by the responsible veterinarian. The safety of this product has not been demonstrated in pregnant mares. Laboratory studies in mice and rabbits have not produced any evidence of teratogenic effects. Reduced fertility was seen in mice at a dose of 5.6 mg/kg body weight per day.
Lactation: The use is not recommended in lactating horses, in which the safety of this product has not been demonstrated. In mice, reduced body weights and survival rates in the progeny were attributed to the pharmacological inhibition of prolactin secretion resulting in lactation failure."
Dianne McFarlane (Equine Pituitary Pars Intermedia Dysfunction Vet. Clin. Equine 27 (2011) 93-113) says that giving pergolide to pregnant mares doesn't seem to cause adverse effects, but it is best discontinued a month before foaling.
Andy Durham and Cathy McGowan were asked about the use of pergolide for pregnant mares in the Boehringer Ingelheim webinar on 04 September 2012. Experience tends to be limited because PPID cases are generally older and often difficult to get in foal. Pregnant mares have been treated with pergolide, but because pergolide could suppress prolactin and therefore milk production, pergolide is often reduced or stopped before lactation. More...
Seasons
There are anecdotal reports that the spring transition may affect mares with PPID (see ECIR Group messages 164441, 154749) and see "insulin" below.
However, in published research there seems to be no evidence that there is any increase in ACTH in the spring:
Effects of pituitary pars intermedia dysfunction (PPID), season, and pasture diet on blood adrenocorticotropic hormone and metabolite concentrations in horses.
Sarah Beth Elliott Masters thesis 2010
See p38 - ACTH concentrations were at their lowest in spring months in both normal and PPID horses (geldings and mares).
See also p56.
Investigating PPID - Liphook Equine Hospital - see graph showing median and IQR ACTH concentrations by month for normal and PPID horses.
Equine Seasonal Cyclicity - Bruce E Eilts - www.vetmed.lsu.edu 2010
Repeatability of prolactin responses to sulpiride in mares and geldings and the effect of pergolide and cabergoline
Rebekah C. Hebert MSc thesis May 2012
"the increasing prolactin concentrations in the spring are involved with loss of the winter hair coat (Thompson et al., 1997) as well as the return of ovarian activity in mares (Nequin et al., 1993)".
Estradiol interactions with dopamine antagonists in mares: prolactin secretion and reproductive traits
Kristian Kandis Kelley MSc Thesis May 2006
"Thompson et al. (1986) reported that horses have higher prolactin levels during the breeding season, with mares having the highest levels. Mares undergoing transition from the anovulatory season in winter to the breeding season experience increases in several hormones, including prolactin."
Insulin
Eleanor M Kellon
Reproductive abnormalities in mares with diet-resistant insulin resistance
No Laminitis Conference Sept 2013 (IVIS)
The ECIR group has had reports of udder enlargement, lactation, irregular cycling and cycles affecting hoof comfort in mares. Several mares with severe insulin resistance that hasn't responded to normal diet restrictions have shown symptoms similar to PCOS in women. There is little evidence that mares have the higher androgen levels found in women with PCOS. Other than around ovulation, FSH levels should be higher than LH in mares, and finding normal to high LH with normal to low FHS can be suggestive. Treatment with estrogens may reduce insulin resistance and laminitis in these mares.
Owners who suspect their mares are affected should join the ECIR Group and/or contact Dr Kellon.
The Impact of Insulin on the Matrix Metalloproteinase System during Equine Follicular Development and Atresia
D R Sessions PhD dissertation 2008
Reprod Fertil Dev 2006;18(6):609-17. (PubMed)
Obesity is associated with altered metabolic and reproductive activity in the mare: effects of metformin on insulin sensitivity and reproductive cyclicity.
Vick M, Sessions D, Murphy B, Kennedy E, Reedy S, Fitzgerald B
"obese mares exhibited a significantly longer duration of the oestrous cycle, significant increases in circulating concentrations of leptin and insulin, and decreased insulin sensitivity and concentrations of thyroxine compared with feed-restricted mares throughout the experiment."
DR Sessions, SE Reedy, MM Vick, BA Murphy, BP Fitzgerald
Development of a model for inducing transient insulin resistance in the mare: Preliminary implications regarding the estrous cycle
J ANIM SCI 2004, 82:2321-2328
(PubMed) Abstract: Peripheral insulin resistance is the failure of proper cellular glucose uptake in response to insulin. Insulin resistance and hyperinsulinemia are associated with several disease states in the horse and reproductive function disturbances in humans, including polycystic ovarian syndrome. To test the hypothesis that insulin resistance (IR) and hyperinsulinemia disrupt the estrous cycle in mares, two experiments were conducted to first develop a model to induce IR and to then examine the effect of this model on the duration of the estrous cycle. In Exp. 1, a hyperinsulinemic-euglycemic clamp (HEC) procedure was performed on seven mares to determine insulin sensitivity before and immediately following infusion of a heparinized lipid solution. The HEC procedure was repeated 1 wk after lipid infusion. Mares developed IR following the lipid infusion (P < 0.05), and some individuals maintained IR for up to 1 wk. Mares also exhibited increased blood insulin both immediately following treatment and 1 wk later (P < 0.05). In Exp. 2, induction of insulin resistance by lipid solution was not accompanied by changes in circulating concentrations of luteinizing hormone, and duration of the luteal phase, compared with the duration of untreated luteal phases. Nonetheless, lipid infusion and the resultant insulin resistance were associated with an increased interovulatory period (P < 0.05), and peak concentrations of progesterone (P < 0.05) were higher during the treated vs. untreated luteal phases of the estrous cycle. The results from the preliminary study suggest that infusion of a lipid solution may induce transient insulin resistance and hyperinsulinemia. The resulting insulin resistance and hyperinsulinemia may modify characteristics of the estrous cycle, perhaps at the level of the ovary.
PCOS Polycystic ovarian syndrome
Morresey P
Metabolic Syndrome in the Pregnant Mare
AAEP Proceedings 2012 Vol 58
In human women, polycystic ovary syndrome (PCOS) is considered a prediabetic state with clinical signs including insulin resistance, obesity and dyslipidemia, and is associated with the development of gestational diabetes. In women, metformin is often prescribed for PCOS and gestational diabetes. "Usage during pregnancy has been shown to improve insulin resistance in hyperinsulinemic PCOS women, with the most benefit seen in those with the greatest insulin resistance and endocrinopathy before conception" (see Glueck et al. 2004 Metformin during pregnancy reduces insulin, insulin resistance, insulin secretion, weight, testosterone and development of gestational diabetes). "Insulin has a major role in the regulation of ovarian steroidogenesis, follicular development, and granulosa cell proliferation. The insulin-like growth factor system is therefore affected, and, as this has been shown crucial to follicle selection and dominance in the mare, disturbances of ovarian function may be seen. Obese mares with reduced insulin sensitivity have been shown to have prolonged interovulatory and luteal phases. A parallel between PCOS in women and disturbances of follicular dynamics in mares can therefore be drawn."
See also Do Equine Metabolic Diseases Affect Reproduction? Erica Larson September 2013 thehorse.com
Munzner, Eyra
Do obese ponies suffer from an equine version of polycystic ovarian syndrome (PCOS)?
Thesis 2010 Charles Sturt University
"Polycystic ovarian syndrome (PCOS) is a highly prevalent and debilitating disease which can have serious consequences for women of reproductive age, including infertility, increased risk of cardiovascular disease and the need for lifelong drug therapy. Further research into the cause and treatment of PCOS has been hampered by the lack of a suitable animal model. It has been identified that pony mares exhibit many of the signs and symptons of PCOS, including obesity, insulin resistance and potential breeding difficulties, and therefore this study aims to, firstly, identify whether pony mares suffer from a condition similar to PCOS, and, secondly, to determine the suitability of pony mares as an animal model for further research into PCOS...."
Other research
Cadario M, Archbald L
Effect of endocrinopathies on fertility in the mare. Part 1: Equine metabolic syndrome
Theriogenology Annual Conference July 2022 published September 2022
Cadario M, Archbald L
Effect of endocrinopathies on fertility in the mare. Part 2: Pituitary pars intermedia dysfunction
Theriogenology Annual Conference July 2022 published September 2022
Ousey JC, Fowden AL, Wilsher S, Allen WR
The effects of maternal health and body condition on the endocrine responses of neonatal foals
Equine Vet J. 2008 Nov;40(7):673-9. doi: 10.2746/042516408x322175. PMID: 19165937
5 first time pregnant mares received a diet to maintain moderate body condition score, and 5 received a diet to maintain a high body condition score. All mares became ill mid-pregnancy and lost around 10% of their weight. During and for one month following their illness/weight loss, insulin and glucose concentrations decreased. Most parameters recorded were similar between foals after birth, but insulin concentrations during glucose tolerance tests were significantly higher in foals from moderate BCS diet mares, when compared to foals from high BCS diet mares. Conclusion: "Acute nutrient restriction in mid gestation caused by maternal illness and inappetence, superimposed on a maintenance feed intake throughout pregnancy, enhanced insulin secretion to glucose in foals." Potential relevance: "Disturbances in neonatal pancreatic beta cell function programmed during pregnancy may predispose foals to metabolic problems in later life."
Hedberg Y, Dalin AM, Forsberg M, Lundeheim N, Hoffmann B, Ludwig C, Kindahl H
Effect of ACTH (tetracosactide) on steroid hormone levels in the mare. Part A: effect in intact normal mares and mares with possible estrous related behavioral abnormalities
Anim Reprod Sci. 2007 Jul;100(1-2):73-91. Epub 2006 Jul 25
Ovariectomized mares and mares with inactive ovaries may show signs of estrus, possibly due to adrenal steroid hormones. Aberrant adrenal hormone production has been suggested as the cause for behavioural changes in some mares. Normal (N) mares and "problem" mares with "deviant estrous bevaviour (P) were given exogenous ACTH or saline. ACTH caused a significant increase in plasma levels of cortisol, progesterone, androstenedione and testosterone in all mares. Problem mares had a lower increase in cortisol and higher increase in progesterone. "The reason for the reduced adreno-cortical reactivity, with a low cortisol response to the ACTH treatment, in the 'problem' mares is unknown, but may indicate a difference in adrenal function as compared to control mares."
Hedberg Y, Dalin AM, Forsberg M, Lundeheim N, Sandh G, Hoffmann B, Ludwig C, Kindahl H
Effect of ACTH (tetracosactide) on steroid hormone levels in the mare. Part B: effect in ovariectomized mares (including estrous behavior)
Anim Reprod Sci. 2007 Jul;100(1-2):92-106
Mares may display estrous signs after ovariectomy. Exogenous ACTH increased cortisol, progesterone, androstenedione and testosterone in normal (N) and ovariectomized (O) mares. Cortisol levels were not different between N and O mares. Androstenedione, progesterone and testosterone levels were lower and increased less after ACTH in O mares.
" It was concluded that ovariectomy affected basal cortisol pattern. Ovarian androstenedione and testosterone contributed to the basal circulating levels and, in the case of androstenedione, was stimulated by ACTH. Endogenous estradiol did not act stimulatory on adrenal gland hormone production in the mare."
Asa CS, Goldfoot DA, Garcia MC, Ginther OJ
Dexamethasone suppression of sexual behavior in the ovariectomized mare
Hormones and Behavior Volume 14, Issue 1, March 1980, Pages 55–64
"estrous behavior seen in ovariectomized mares may be due to steroids from the adrenal cortex" ... "other adrenal steroids, e.g., androgens, may be involved in estrous behavior in the untreated, ovariectomized mare".
P M McCue
Review of ovarian abnormalities in the mare
AAEP Proceedings Vol 44 1998
Fowden AL, Comline RS, Silver M
Insulin secretion and carbohydrate metabolism during pregnancy in the mare
Equine Vet J. 1984 Jul;16(4):239-46. doi: 10.1111/j.2042-3306.1984.tb01919.x. PMID: 6383807 (Full paper: Deepdyve)
Medicines and drugs
In the UK and the EU, when a veterinary medicine is licensed in that country for that disease in that animal, the licensed medicine must be used - see Cascade Guide for veterinarians if NO authorised medicinal product is available (FVE 2013).
Datasheets for medicines/drugs
UK
Veterinary Medicines Directorate Product Information Database
NOAH Compendium of Authorised Veterinary Medicines
USA
National Library of Medicine
Medicines/treatments for PPID:
Pergolide (Prascend)
Pain relieving medicines
NSAiDs e.g. Phenylbutazone (Bute, Equipalazone), Suxibuzone (Danilon) and Meloxicam (Metacam) are often the first line pain relieving medicines given to horses with laminitis. Acetaminophen (Paracetamol) is also given.
Phenylbutazone (Bute, Equipalazone)
Acetaminophen (Paracetamol)
Danilon (Suxibuzone) is metabolized to phenylbutazone inside the horse. Research by Frank Andrews et al. (2009) found no difference in gastric ulcer formation when maintenance doses of phenylbutazone and suxibuzone were administered.
Medicines/treatments for EMS/insulin dysregulation
Note that there is currently no published controlled research showing efficacy of any medication for EMS/insulin dysregulation, and experts suggest that "the mainstay for treatment of EMS is weight reduction, with a combination of dietary modification and exercise in horses without painful or unstable laminitis."
Metformin
Levothyroxine
SGLT-2 inhibitors
Durham AE
Therapeutics for Equine Endocrine Disorders
Vet Clin North Am Equine Pract. 2017 Apr;33(1):127-139. doi: 10.1016/j.cveq.2016.11.003. Epub 2017 Feb 9
Do sedation drugs affect ACTH, insulin, glucose blood results?
In his 2015 webinar "You've diagnosed PPID - now what?" Andy Durham of Liphook Equine Hospital said that when blood samples have been taken before and after sedation, it is not unusual to see abrupt increases and decreases in ACTH post-sedation. Sedation appears to have the capacity to alter ACTH, and until further research is carried out, current advice is that blood should not be collected for ACTH testing after a horse has been sedated.
In the UK and the EU, when a veterinary medicine is licensed in that country for that disease in that animal, the licensed medicine must be used - see Cascade Guide for veterinarians if NO authorised medicinal product is available (FVE 2013).
Datasheets for medicines/drugs
UK
Veterinary Medicines Directorate Product Information Database
NOAH Compendium of Authorised Veterinary Medicines
USA
National Library of Medicine
Medicines/treatments for PPID:
Pergolide (Prascend)
Pain relieving medicines
NSAiDs e.g. Phenylbutazone (Bute, Equipalazone), Suxibuzone (Danilon) and Meloxicam (Metacam) are often the first line pain relieving medicines given to horses with laminitis. Acetaminophen (Paracetamol) is also given.
Phenylbutazone (Bute, Equipalazone)
Acetaminophen (Paracetamol)
Danilon (Suxibuzone) is metabolized to phenylbutazone inside the horse. Research by Frank Andrews et al. (2009) found no difference in gastric ulcer formation when maintenance doses of phenylbutazone and suxibuzone were administered.
Medicines/treatments for EMS/insulin dysregulation
Note that there is currently no published controlled research showing efficacy of any medication for EMS/insulin dysregulation, and experts suggest that "the mainstay for treatment of EMS is weight reduction, with a combination of dietary modification and exercise in horses without painful or unstable laminitis."
Metformin
Levothyroxine
SGLT-2 inhibitors
Durham AE
Therapeutics for Equine Endocrine Disorders
Vet Clin North Am Equine Pract. 2017 Apr;33(1):127-139. doi: 10.1016/j.cveq.2016.11.003. Epub 2017 Feb 9
Do sedation drugs affect ACTH, insulin, glucose blood results?
In his 2015 webinar "You've diagnosed PPID - now what?" Andy Durham of Liphook Equine Hospital said that when blood samples have been taken before and after sedation, it is not unusual to see abrupt increases and decreases in ACTH post-sedation. Sedation appears to have the capacity to alter ACTH, and until further research is carried out, current advice is that blood should not be collected for ACTH testing after a horse has been sedated.
Kritchevsky JE, Muir GS, Leschke DHZ, Hodgson JK, Hess EK, Bertin FR
Blood glucose and insulin concentrations after alpha-2-agonists administration in horses with and without insulin dysregulation
J Vet Intern Med. 2020 Mar;34(2):902-908. doi: 10.1111/jvim.15747. Epub 2020 Feb 26
Keywords: detomidine, endocrinology, equine, metabolism, pancreas, xylazine
Alpha-2-agonists Detomadine and Xylazine are commonly used for horses, alone or in combination with other sedatives or pain relief, to provide sedation and pain relief. Both Detomadine and Xylazine induced hyperglycaemia in non insulin dysregulation (NID) and insulin dysregulation (ID) horses, with ID horses having a longer increase. In both NID and ID horses, both drugs induced an initial mild decrease in serum insulin followed by an increase in insulin.
Metalloproteinases - MMPs (matrix metalloproteinases), ADAM and ADAMTS proteins
Metalloproteinases (MPs) and tissue inhibitors of metalloproteinases (TIMPs) are proteolytic enzymes that play an important role in the maintenance of the extracellular matrix (ECM) structure through degradation and remodelling. The ECM provides a scaffold for the cellular components of tissues, and joins dermal and epidermal tissues together, such as the laminae in the foot. Metalloproteinases include MMPs (matrix metalloproteinases), ADAM proteins and ADAMTS proteins. MPs affect collagen, cytokines and growth factors and play a role in both normal (physiological) and disease (pathological) processes in the ECM, with MP activity normally being tightly controlled by TIMPs to prevent tissue damage caused by unregulated MP activity.
The activity of MPs (specifically MMP-2, MMP-9, MMP-14 and ADAMTS-4) has been shown to increase in the developmental phase of sepsis-related (inflammatory) laminitis. However, Melody de Laat (de Laat et al. 2011) compared the lamellar tissue of horses with insulin-induced laminitis to control horses and found no increase in MMP-2, MTI-MMP, ADAMTS-4 and TIMP-3, suggesting that these MPs "do not appear to play a significant role in the pathogenesis of insulin-induced laminitis". Although not increased during the developmental phase, an increase in (mostly inactive) neutrophil-associated MMP-9 was found in horses that developed laminitis after 48 hours of induced hyperinsulinaemia
In her 2016 PhD thesis The prevalence and histopathy of endocrinopathic laminitis in horses, Ninja Karikoski described de Laat's work, and concluded "it is unlikely that metalloproteases have a significant role in the development of hyperinsulinemic laminitis."
Research
Ninja Karikoski Dissertation May 2016
The prevalence and histopathology of endocrinopathic laminitis in horses
Visser MB, Pollitt CC
The timeline of metalloprotease events during oligofructose induced equine laminitis development
Equine Veterinary Journal. doi: 10.1111/j.2042-3306.2011.00393.x (2011)
"MMPs, historically thought to cause laminitis, do not appear to play an initiating role in the lamellar lesion. Other host derived proteases and degradation of alternative lamellar matrix components need to be considered."
Veterinary Immunology and Immunopathology 140 (2011) 275–281
The developmental and acute phases of insulin-induced laminitis involve minimal metalloproteinase activity
de Laat MA, Kyaw-Tanner MT, Nourian AR, McGowan CM, Sillence MN, Pollitt CC
"MMP-2, MT1-MMP, TIMP-3 and ADAMTS-4 do not appear to play a significant role in the pathogenesis of insulin-induced laminitis. The increased expression of MMP-9 may be associated with the infiltration of inflammatory leukocytes, or may be a direct result of hyperinsulinaemia. The exact role of MMP-9 in basement membrane degradation in laminitis is uncertain as it appears to be present largely in the inactive form "
Lee Ann Fugler PhD dissertation 2009
Matrix Metalloproteinases in the Equine Systemic Inflammatory Response: Implications for Equine Laminitis
Loftus JP, Johnson PJ, Belknap JK, Pettigrew A, Black SJ
Leukocyte-derived and endogenous matrix metalloproteinases in the lamellae of horses with naturally acquired and experimentally induced laminitis
Vet Immunol Immunopathol. 2009 Jun 15;129(3-4):221-30. doi: 10.1016/j.vetimm.2008.11.003. Epub 2008 Nov 7
Lamellar samples were taken from 12 horses with naturally acquired laminitis, 7 horses that developed Obel grade 3 laminitis after being force fed starch, and 4 that didn't develop lameness after being force fed starch, and examined for MMPs.
Horses with no laminitis and chronic laminitis had low levels of MMP-9 and MMP-2.
Horses with starch-induced laminitis had varying elevated levels of proMMP-9 and MMP-2.
MMP-9 was associated with (produced by) inflammatory leukocytes.
Leukocyte infiltration and dysregulation of MMP-2 appeared to be independent of each other, suggesting distinct inducers.
Metformin
Metformin (Glucophage) is a biguanide/anti-hyperglycaemic drug licensed for humans with metabolic syndrome/type 2 diabetes mellitus that is sometimes prescribed for horses with hyperinsulinaemia/insulin dysregulation (ID)/Equine Metabolic Syndrome (EMS). In humans, Metformin affects glucose uptake from the intestine, causing glucose to be metabolized into lactate, but the exact interaction between Metformin and glucose has not been established.
Metformin is poorly absorbed by horses, with only 7.1% bioavailability reported when Metformin was given orally to fasted horses, and 3.9% when given to fed horses (Hustace et al. 2009).
Metformin is generally available in 1000 mg, 850 mg or 500 mg tablets. The slow release form of Metformin should not be used for horses.
Pharmacokinetics and side effects
In humans, Metformin is excreted by the kidneys and does not undergo hepatic (liver) metabolism - its use in patients with renal insufficiency (kidney problems) is not recommended. In humans, gastrointestinal side effects are frequently reported.
In humans Metformin is associated with vitamin B12 deficiency. However, humans obtain vitamin B12 from their diet, whereas horses synthesize B12 in their digestive tract. Intestinal B12 synthesis requires the essential mineral cobalt, but note that the normal diet is likely to meet cobalt requirements and neither cobalt nor vitamin B12 deficiency have ever been recorded or experimentally induced in horses (but research into B12 levels in horses taking Metformin has not been carried out).
Metformin is not licensed for horses, and adverse effects are not recorded. TLS has had owners report incidence of mouth ulcers when Metformin is syringed into the mouth.
Metformin - www.drugs.com
Metformin (Glucophage) data sheet
Is Metformin necessary/effective for horses with EMS/ID?
The short answer is no, there is no research showing that Metformin improves insulin sensitivity when given to horses. Colmer et al. 2023 gave 30 mg/kg metformin to horses with insulin dysregulation and then carried out an oral sugar test using Karo Light corn syrup, and found no significant effect on plasma glucose, insulin or C-peptide after giving metformin compared to controls. In the only research that shows any benefit, horses given Metformin before a high sugar meal had lower blood levels of glucose and insulin than horses not given metformin (Rendle et al. 2013). However - obviously - horses with EMS/ID shouldn't be given high sugar meals, and the authors of that paper concluded that the potential benefits of giving Metformin to horses fed an appropriate low sugar/starch diet may be questionable. In 2015, Ruth Morgan et al. wrote: "The mainstay for treatment of EMS is weight reduction, with a combination of dietary modification and exercise in horses without painful or unstable laminitis."
Similarly, in a 2017 webinar, Nicola Menzies-Gow from the Royal Veterinary College suggested that management - low sugar/starch diet, weight loss if necessary and exercise when able - should be the treatment for EMS, not medication. Medical therapy should be used very carefully - if at all - for a maximum of 3 to 6 months, and is mostly suggested for owners who are looking for a pill to fix things rather than improve their management or wait for improvements from management changes. Around 2011 Metformin was being used for horses that couldn't exercise - described as "exercise in a tablet" - but it has gone out of fashion now that it is known that only up to around 7% of Metformin is absorbed by horses. Studies have shown no effect on insulin resistant horses - it has not been shown to improve insulin sensitivity in horses. The only beneficial effect shown in research on horses is that it reduced gastrointestinal glucose absorption and therefore insulinaemic response, when given at 30 mg/kg bodyweight 30 minutes before a large amount of sugar. Some vets have suggested giving Metformin before turning horses out to graze, but Dr Menzies-Gow said she thought it might be "a bit dangerous to rely on metformin to counter the effect of grass".
TLS opinion: concentrate on correct diet, weight loss and correcting and supporting feet and removing the cause so that a horse can return to exercise. This is proven to improve insulin sensitivity (see Morgan et al. 2016). Metformin is not. Metformin is not licensed for horses, and adverse effects are not recorded. TLS has had owners report incidence of mouth ulcers when Metformin is syringed into the mouth.
Might Metformin play any role in preventing laminitis?
Metformin may reduce cell growth in response to IGF-1:
Tosca L, Ramé C, Chabrolle C, Tesseraud S, Dupont J
Metformin decreases IGF1-induced cell proliferation and protein synthesis through AMP-activated protein kinase in culturedbovine granulosa cells.
Reproduction. 2010 Feb;139(2):409-18
Research
Colmer SF, Adams AA, Adam E, Miller R, Stefanovski D, Kulp JC, van Eps A.
The effect of pre-dosing with metformin on the insulin response to oral sugar in insulin-dysregulated horses.
Equine Vet J. 2023 Aug 6. doi: 10.1111/evj.13979. Epub ahead of print. PMID: 37545128.
Keywords: EMS, equine metabolic syndrome, glucose regulation, horse, hyperinsulinaemia, insulin secretion.
Ericsson AC, Johnson PJ, Gieche LM, Zobrist C, Bucy K, Townsend KS, Martin LM, LaCarrubba AM.
The Influence of Diet Change and Oral Metformin on Blood Glucose Regulation and the Fecal Microbiota of Healthy Horses.
Animals (Basel). 2021 Apr 1;11(4):976. doi: 10.3390/ani11040976. PMID: 33915682; PMCID: PMC8065426.
Keywords: equine; glucose tolerance; metabolic syndrome.
de Laat Ma, Sillence MN
A review of recent developments in the pharmagological prevention and treatment of endocrinopathic laminitis
Animal Production Science published online 16 June 2020. doi.org/10.1071/AN19491
Morgan R, Keen J, McGowan C
Equine metabolic syndrome
Veterinary Record Aug 2015;177:173-179 doi:10.1136/vr.103226
"The mainstay for treatment of EMS is weight reduction, with a combination of dietary modification and exercise in horses without painful or unstable laminitis."
Rendle DI, Rutledge F, Hughes KJ, Heller J, Durham AE
Effects of metformin hydrochloride on blood glucose and insulin responses to oral dextrose in horses
Equine Vet J. 2013 Nov;45(6):751-754
Giving 30 mg/kg bodyweight metformin 60 minutes before a rice bran feed containing 0.5 mg dextrose (glucose) per kg bodyweight led to reduced glucose and insulin levels compared to controls. Metformin may accumulate in the intestine at much higher levels than in blood. In rats, Metformin delays the absorption of glucose by the intestine and increases glucose utilization by intestinal tissue. In mice, concentrations of Metformin in intestinal tissue decline rapidly after peaking 2 hours after administration. "Whether the effects of metformin on the equine intestine are of sufficient duration to result in clinical benefit remains to be determined." It is hyperinsulinaemia rather than insulin resistance per se that appears to cause laminitis in horses. The paper suggests that the insulin lowering effects of Metformin might reduce diet-induced hyperinsulinaemia even in the absence of insulin sensitizing effects. It theorizes that by reducing glucose absorption, Metformin may also lower calorie intake and help weight loss (however, in horses, presumably glucose not absorbed in the small intestine will pass to the hind gut where it will be fermented to volatile fatty acids, therefore still provide calories. Also might this risk acidosis, as normally very little glucose will pass to the hind gut?). "The potential benefit of these effects in horses fed appropriate forage that is low in nonstructural carbohydrates versus more glycaemic diets, such as grass, forage with a high nonstructural carbohydrate concentration and cereals, may be questionable".
The horses used in the research were all healthy, and although insulin resistance was induced by giving them dexamethasone, this may not reflect natural insulin resistance/EMS.
"In conclusion, the present study indicates that orally administered metformin reduces the glycaemic and insulinaemic responses to orally administered dextrose in horses. Further work is required to determine whether these effects may translate into clinical benefits in horses with EMS and hyperinsulinaemia."
Durham AE, Rendle DI, Rutledge F, Heller J, Hughes KJ
The effects of Metformin Hydrochloride on intestinal glucose absorption and use of tests for hyperinsulinaemia
ACVIM Research Report Submissions 2012
A dose of 30 mg/kg BW Metformin given 30 minutes before an oral glucose test significantly reduced glucose absorption and the subsequent insulin response in all horses.
Rendle D, Cathcart M, Duz M, Heller J, Hughes K, Love S, Sutton D
Effects of Metformin on insulin sensitivity assessed using a combined glucose insulin test in 11 horses with Equine Metabolic Syndrome
J Vet Intern Med 2012;26:428-429 (5th Congress ECEIM 2012)
A retrospective study looked at 11 horses with a history of laminitis, body condition score (BCS) >5/9 and insulin resistance diagnosed by CGIT. The horses had dietary restriction plus treatment with metformin at an average (mean) dose of 24 mg/kg bodyweight (how often per day?) for an average (mean) of 28 weeks (range was 9 to 91 weeks). No controls were used. At the end of the treatment there were no significant changes in body weight, BCS or insulin sensitivityn. There were slight but not significant improvements in RISQI, G:I ratio and MIRG, but slight but not significant increases in time taken for glucose to return to baseline and area under the glucose curve. The research concluded: "Measured and calculated indices of IS in the 11 horses with EMS described in this study did not change significantly following instigation of treatment with metformin and dietary restriction, suggesting that metformin may not be of clinical benefit in this species."
Vet J. 2012 Jan;191(1):79-84. Epub 2011 Feb 23
The effect of oral metformin on insulin sensitivity in insulin-resistant ponies.
Tinworth K, Boston R, Harris P, Sillence M, Raidal S, Noble G
After giving non-obese IR ponies 15 mg/kg BW metformin 2 x day for 21 days, "there was no significant change in SI, Sg, AIRg, DI, BW, BCS or CNS in response to metformin, or over time in the control group. There were no measurable benefits of metformin on SI, consistent with recent work showing that the bioavailability of metformin in horses is poor, and chronic dosing may not achieve therapeutic blood concentrations."
See also p35 of the Proceedings of the Australasian Equine Science Symposium 2010:
Efficacy of oral metformin in insulin-resistant ponies
Durham AE
Metformin in equine metabolic syndrome: An enigma or a dead duck?
Vet J. 2012 Jan;191(1):17-8. Epub 2011 Aug 31.
Chameroy KA, PhD dissertation 2010
Diagnosis and Management of Horses with Equine Metabolic Syndrome (EMS)
Metformin pages 40-42
Effects of metformin hydrochloride on glucose dynamics during transition to grass paddocks in insulin-resistant horses pages 92-104
Am J Vet Res. 2010 Oct;71(10):1201-6.
Pharmacokinetics of metformin after enteral administration in insulin-resistant ponies.
Tinworth K, Edwards S, Noble G, Harris P, Sillence M, Hackett L
Durham A
The pharmacologic basis for the treatment of endocrinopathic laminitis
Vet Clin North Am Equine Pract. 2010 Aug;26(2):303-14
Full paper
Am J Vet Res. 2009 May;70(5):665-8.
Pharmacokinetics and bioavailability of metformin in horses.
Hustace J, Firshman A, Mata J
The oral bioavailability of Metformin in horses was reported as only 7.1 per cent in unfed horses and 3.9 per cent in fed horses.
Equine Veterinary Journal Voi 40, Issue 5, pages 493-500, July 2008
The effect of metformin on measurements of insulin sensitivity and β cell response in 18 horses and ponies with insulin resistance
Durham A, Rendle D, Newton J
This study suggested an improvement in basal measures of insulin sensitivity in a small number of insulin resistant horses when Metformin was given at a dose of 15 mg/kg bodyweight, but controls were not used, making the research invalid.
Reprod Fertil Dev 2006;18(6):609-17.
Obesity is associated with altered metabolic and reproductive activity in the mare: effects of metformin on insulin sensitivity and reproductive cyclicity.
Vick M, Sessions D, Murphy B, Kennedy E, Reedy S, Fitzgerald B
Metformin is poorly absorbed by horses, with only 7.1% bioavailability reported when Metformin was given orally to fasted horses, and 3.9% when given to fed horses (Hustace et al. 2009).
Metformin is generally available in 1000 mg, 850 mg or 500 mg tablets. The slow release form of Metformin should not be used for horses.
Pharmacokinetics and side effects
In humans, Metformin is excreted by the kidneys and does not undergo hepatic (liver) metabolism - its use in patients with renal insufficiency (kidney problems) is not recommended. In humans, gastrointestinal side effects are frequently reported.
In humans Metformin is associated with vitamin B12 deficiency. However, humans obtain vitamin B12 from their diet, whereas horses synthesize B12 in their digestive tract. Intestinal B12 synthesis requires the essential mineral cobalt, but note that the normal diet is likely to meet cobalt requirements and neither cobalt nor vitamin B12 deficiency have ever been recorded or experimentally induced in horses (but research into B12 levels in horses taking Metformin has not been carried out).
Metformin is not licensed for horses, and adverse effects are not recorded. TLS has had owners report incidence of mouth ulcers when Metformin is syringed into the mouth.
Metformin - www.drugs.com
Metformin (Glucophage) data sheet
Is Metformin necessary/effective for horses with EMS/ID?
The short answer is no, there is no research showing that Metformin improves insulin sensitivity when given to horses. Colmer et al. 2023 gave 30 mg/kg metformin to horses with insulin dysregulation and then carried out an oral sugar test using Karo Light corn syrup, and found no significant effect on plasma glucose, insulin or C-peptide after giving metformin compared to controls. In the only research that shows any benefit, horses given Metformin before a high sugar meal had lower blood levels of glucose and insulin than horses not given metformin (Rendle et al. 2013). However - obviously - horses with EMS/ID shouldn't be given high sugar meals, and the authors of that paper concluded that the potential benefits of giving Metformin to horses fed an appropriate low sugar/starch diet may be questionable. In 2015, Ruth Morgan et al. wrote: "The mainstay for treatment of EMS is weight reduction, with a combination of dietary modification and exercise in horses without painful or unstable laminitis."
Similarly, in a 2017 webinar, Nicola Menzies-Gow from the Royal Veterinary College suggested that management - low sugar/starch diet, weight loss if necessary and exercise when able - should be the treatment for EMS, not medication. Medical therapy should be used very carefully - if at all - for a maximum of 3 to 6 months, and is mostly suggested for owners who are looking for a pill to fix things rather than improve their management or wait for improvements from management changes. Around 2011 Metformin was being used for horses that couldn't exercise - described as "exercise in a tablet" - but it has gone out of fashion now that it is known that only up to around 7% of Metformin is absorbed by horses. Studies have shown no effect on insulin resistant horses - it has not been shown to improve insulin sensitivity in horses. The only beneficial effect shown in research on horses is that it reduced gastrointestinal glucose absorption and therefore insulinaemic response, when given at 30 mg/kg bodyweight 30 minutes before a large amount of sugar. Some vets have suggested giving Metformin before turning horses out to graze, but Dr Menzies-Gow said she thought it might be "a bit dangerous to rely on metformin to counter the effect of grass".
TLS opinion: concentrate on correct diet, weight loss and correcting and supporting feet and removing the cause so that a horse can return to exercise. This is proven to improve insulin sensitivity (see Morgan et al. 2016). Metformin is not. Metformin is not licensed for horses, and adverse effects are not recorded. TLS has had owners report incidence of mouth ulcers when Metformin is syringed into the mouth.
Might Metformin play any role in preventing laminitis?
Metformin may reduce cell growth in response to IGF-1:
Tosca L, Ramé C, Chabrolle C, Tesseraud S, Dupont J
Metformin decreases IGF1-induced cell proliferation and protein synthesis through AMP-activated protein kinase in culturedbovine granulosa cells.
Reproduction. 2010 Feb;139(2):409-18
Research
Colmer SF, Adams AA, Adam E, Miller R, Stefanovski D, Kulp JC, van Eps A.
The effect of pre-dosing with metformin on the insulin response to oral sugar in insulin-dysregulated horses.
Equine Vet J. 2023 Aug 6. doi: 10.1111/evj.13979. Epub ahead of print. PMID: 37545128.
Keywords: EMS, equine metabolic syndrome, glucose regulation, horse, hyperinsulinaemia, insulin secretion.
Ericsson AC, Johnson PJ, Gieche LM, Zobrist C, Bucy K, Townsend KS, Martin LM, LaCarrubba AM.
The Influence of Diet Change and Oral Metformin on Blood Glucose Regulation and the Fecal Microbiota of Healthy Horses.
Animals (Basel). 2021 Apr 1;11(4):976. doi: 10.3390/ani11040976. PMID: 33915682; PMCID: PMC8065426.
Keywords: equine; glucose tolerance; metabolic syndrome.
de Laat Ma, Sillence MN
A review of recent developments in the pharmagological prevention and treatment of endocrinopathic laminitis
Animal Production Science published online 16 June 2020. doi.org/10.1071/AN19491
Morgan R, Keen J, McGowan C
Equine metabolic syndrome
Veterinary Record Aug 2015;177:173-179 doi:10.1136/vr.103226
"The mainstay for treatment of EMS is weight reduction, with a combination of dietary modification and exercise in horses without painful or unstable laminitis."
Rendle DI, Rutledge F, Hughes KJ, Heller J, Durham AE
Effects of metformin hydrochloride on blood glucose and insulin responses to oral dextrose in horses
Equine Vet J. 2013 Nov;45(6):751-754
Giving 30 mg/kg bodyweight metformin 60 minutes before a rice bran feed containing 0.5 mg dextrose (glucose) per kg bodyweight led to reduced glucose and insulin levels compared to controls. Metformin may accumulate in the intestine at much higher levels than in blood. In rats, Metformin delays the absorption of glucose by the intestine and increases glucose utilization by intestinal tissue. In mice, concentrations of Metformin in intestinal tissue decline rapidly after peaking 2 hours after administration. "Whether the effects of metformin on the equine intestine are of sufficient duration to result in clinical benefit remains to be determined." It is hyperinsulinaemia rather than insulin resistance per se that appears to cause laminitis in horses. The paper suggests that the insulin lowering effects of Metformin might reduce diet-induced hyperinsulinaemia even in the absence of insulin sensitizing effects. It theorizes that by reducing glucose absorption, Metformin may also lower calorie intake and help weight loss (however, in horses, presumably glucose not absorbed in the small intestine will pass to the hind gut where it will be fermented to volatile fatty acids, therefore still provide calories. Also might this risk acidosis, as normally very little glucose will pass to the hind gut?). "The potential benefit of these effects in horses fed appropriate forage that is low in nonstructural carbohydrates versus more glycaemic diets, such as grass, forage with a high nonstructural carbohydrate concentration and cereals, may be questionable".
The horses used in the research were all healthy, and although insulin resistance was induced by giving them dexamethasone, this may not reflect natural insulin resistance/EMS.
"In conclusion, the present study indicates that orally administered metformin reduces the glycaemic and insulinaemic responses to orally administered dextrose in horses. Further work is required to determine whether these effects may translate into clinical benefits in horses with EMS and hyperinsulinaemia."
Durham AE, Rendle DI, Rutledge F, Heller J, Hughes KJ
The effects of Metformin Hydrochloride on intestinal glucose absorption and use of tests for hyperinsulinaemia
ACVIM Research Report Submissions 2012
A dose of 30 mg/kg BW Metformin given 30 minutes before an oral glucose test significantly reduced glucose absorption and the subsequent insulin response in all horses.
Rendle D, Cathcart M, Duz M, Heller J, Hughes K, Love S, Sutton D
Effects of Metformin on insulin sensitivity assessed using a combined glucose insulin test in 11 horses with Equine Metabolic Syndrome
J Vet Intern Med 2012;26:428-429 (5th Congress ECEIM 2012)
A retrospective study looked at 11 horses with a history of laminitis, body condition score (BCS) >5/9 and insulin resistance diagnosed by CGIT. The horses had dietary restriction plus treatment with metformin at an average (mean) dose of 24 mg/kg bodyweight (how often per day?) for an average (mean) of 28 weeks (range was 9 to 91 weeks). No controls were used. At the end of the treatment there were no significant changes in body weight, BCS or insulin sensitivityn. There were slight but not significant improvements in RISQI, G:I ratio and MIRG, but slight but not significant increases in time taken for glucose to return to baseline and area under the glucose curve. The research concluded: "Measured and calculated indices of IS in the 11 horses with EMS described in this study did not change significantly following instigation of treatment with metformin and dietary restriction, suggesting that metformin may not be of clinical benefit in this species."
Vet J. 2012 Jan;191(1):79-84. Epub 2011 Feb 23
The effect of oral metformin on insulin sensitivity in insulin-resistant ponies.
Tinworth K, Boston R, Harris P, Sillence M, Raidal S, Noble G
After giving non-obese IR ponies 15 mg/kg BW metformin 2 x day for 21 days, "there was no significant change in SI, Sg, AIRg, DI, BW, BCS or CNS in response to metformin, or over time in the control group. There were no measurable benefits of metformin on SI, consistent with recent work showing that the bioavailability of metformin in horses is poor, and chronic dosing may not achieve therapeutic blood concentrations."
See also p35 of the Proceedings of the Australasian Equine Science Symposium 2010:
Efficacy of oral metformin in insulin-resistant ponies
Durham AE
Metformin in equine metabolic syndrome: An enigma or a dead duck?
Vet J. 2012 Jan;191(1):17-8. Epub 2011 Aug 31.
Chameroy KA, PhD dissertation 2010
Diagnosis and Management of Horses with Equine Metabolic Syndrome (EMS)
Metformin pages 40-42
Effects of metformin hydrochloride on glucose dynamics during transition to grass paddocks in insulin-resistant horses pages 92-104
Am J Vet Res. 2010 Oct;71(10):1201-6.
Pharmacokinetics of metformin after enteral administration in insulin-resistant ponies.
Tinworth K, Edwards S, Noble G, Harris P, Sillence M, Hackett L
Durham A
The pharmacologic basis for the treatment of endocrinopathic laminitis
Vet Clin North Am Equine Pract. 2010 Aug;26(2):303-14
Full paper
Am J Vet Res. 2009 May;70(5):665-8.
Pharmacokinetics and bioavailability of metformin in horses.
Hustace J, Firshman A, Mata J
The oral bioavailability of Metformin in horses was reported as only 7.1 per cent in unfed horses and 3.9 per cent in fed horses.
Equine Veterinary Journal Voi 40, Issue 5, pages 493-500, July 2008
The effect of metformin on measurements of insulin sensitivity and β cell response in 18 horses and ponies with insulin resistance
Durham A, Rendle D, Newton J
This study suggested an improvement in basal measures of insulin sensitivity in a small number of insulin resistant horses when Metformin was given at a dose of 15 mg/kg bodyweight, but controls were not used, making the research invalid.
Reprod Fertil Dev 2006;18(6):609-17.
Obesity is associated with altered metabolic and reproductive activity in the mare: effects of metformin on insulin sensitivity and reproductive cyclicity.
Vick M, Sessions D, Murphy B, Kennedy E, Reedy S, Fitzgerald B
Microbiome
The microbiome comprises a large complex mixture of bacteria, viruses, protozoa, fungi and archaea which are important to the overall health of the horse. Horses rely on the gut microbiome to produce nutrients and energy (short chain or volatile fatty acids) from ingested complex carbohydrates. In horses, the microbiome has been implicated in diseases including laminitis (Milinovich et al. 2010) and EMS (Elzinga et al. 2016). The microbiota is highly variable between horses and within the same horse, changes quickly in response to diet changes, is sensitive to eating starch, fibre and fat and is affected by age and exercise. Microbiome changes in response to changes in grass, addition of haylage and environmental conditions that were considered to be normal and did not cause any clinical abnormalities were recorded in horses kept on pasture (Salem et al. 2018). The faecal microbiome (i.e. found in dung) is considered to represent the microbiota population of the lower hindgut.
Johnson A, Biddle A
2 Evaluation of the microbiome effects of easy and hard keeper horses with the application of the Equine Keeper Status Scale
JEVS May 2021 Vol 100 Proceedings of the Virtual Equine Science Symposium 1-4 June 2021 103465
Presentation by Alexa Johnson
The horse's unique microbiome contains bacteria, archaea, protozoa and anaerobic fungi, and is responsible for fermenting fibrous feed to volatile fatty acids (VFAs), which it is estimated can provide up to 70% of a horse's energy requirements.
Leng J, McNally S, Walton G, Swann J, Proudman C, Argo C, Emery S, La Ragione R, Eustace R.
Hay vs. haylage; forage type influences the equine urinary metabonome and faecal microbiota.
Equine Vet J. 2021 Apr 26. doi: 10.1111/evj.13456. Epub ahead of print. PMID: 33900659.
Tuniyazi M, He J, Guo J, Li S, Zhang N, Hu Z, Fu Y
Changes of microbial and metabolome of the equine hindgut during oligofructose-induced laminitis
BMC Vet Res 17, 11 (2021). https://doi.org/10.1186/s12917-020-02686-9
Fitzgerald DM, Spence RJ, Stewart ZK, Prentis PJ, Sillence MN, de Laat MA.
The effect of diet change and insulin dysregulation on the faecal microbiome of ponies.
J Exp Biol. 2020 Apr 1;223(Pt 7):jeb219154. doi: 10.1242/jeb.219154. PMID: 32098884.
Keywords: 16S rRNA; Endocrine; Equine metabolic syndrome; Glucagon-like peptide-1; Hindgut; Horse.
Morrison PK, Newbold CJ, Jones E, Worgan HJ, Grove-White DH, Dugdale AH, Barfoot C, Harris PA, Argo CM
The Equine Gastrointestinal Microbiome: Impacts of Age and Obesity
Front Microbiol. 07 Dec 2018 9:3017. doi: 10.3389/fmicb.2018.03017
Biddle AS, Tomb JF, Fan Z.
Microbiome and Blood Analyte Differences Point to Community and Metabolic Signatures in Lean and Obese Horses.
Front Vet Sci. 2018 Sep 20;5:225. doi: 10.3389/fvets.2018.00225. PMID: 30294603; PMCID: PMC6158370.
Keywords: 16S rRNA; equine gut microbiome; glucose; insulin; leptin; network analysis; obesity; triglycerides.
Obese horses had greater phyla diversity and greater richness of gut bacteria than lean horses, and higher blood glucose, cortisol, triglycerides and leptin. Taxa associated with a healthy gut were correlated with obesity: Propionibacteriaceae (a propionate producer), Butyrivibrio species (butyrate producers), Ruminococcaceae (fibre degraders) and Sutterella species. There was no correlation between resting insulin and microbiome taxa abundance.
Salem SE, Maddox TW, Berg A, Antczak P, Ketley JM, Williams JN, Archer DC
Variation in faecal microbiota in a group of horses managed at pasture over a 12-month period
Sci Rep 8, 8510 (2018). https://doi.org/10.1038/s41598-018-26930-3
Studying dung collected every 14 days from 7 healthy horses kept at grass (with supplemental haylage when grass was sparse) showed that the fecal microbiota constantly changed in response to changes in the grass and feeding of haylage and weather conditions over 12 months, and suggested that fluctuation in the microbiota is a normal response to dietary and environmental changes. There was significant difference in faecal microbiota between horses on the same diet of pasture and haylage. Ambient temperature and rainfall affected the faecal microbiota - this could be because of changes in the grass, or the effect of weather on environmental bacteria eaten with the grass (which have been shown to survive enzymatic digestion in the stomach and to colonise the hindgut resulting in shifts in gut microbiota).
The faecal microbiota was dominated by members of the Firmicutes and Bacteroidetes phyla (with Fibrobacteres, Spirochaetes, Verrucomicrobia and Proteobacteria being the other significant bacterial phyla identified). Other studies have found horse faecal microbiota dominated by Firmicutes and Verrucomicrobia phyla, but the sequencing technology used may account for variation in results.
When haylage was fed, the relative abundance of members of the phylum Fibrobacters and Spirochaetes increased, and Firmicutes decreased. Fibrobacteres is effective at hydrolysing plant cellulose.
The research concluded that the equine microbiome is highly dynamic, responds to dietary factors and ambient environmental conditions, changed over 12 months but did not cause any clinical abnormalities.
The microbiome comprises a large complex mixture of bacteria, viruses, protozoa, fungi and archaea which are important to the overall health of the horse. Horses rely on the gut microbiome to produce nutrients and energy (short chain or volatile fatty acids) from ingested complex carbohydrates. In horses, the microbiome has been implicated in diseases including laminitis (Milinovich et al. 2010) and EMS (Elzinga et al. 2016). The microbiota is highly variable between horses and within the same horse, changes quickly in response to diet changes, is sensitive to eating starch, fibre and fat and is affected by age and exercise. Microbiome changes in response to changes in grass, addition of haylage and environmental conditions that were considered to be normal and did not cause any clinical abnormalities were recorded in horses kept on pasture (Salem et al. 2018). The faecal microbiome (i.e. found in dung) is considered to represent the microbiota population of the lower hindgut.
Johnson A, Biddle A
2 Evaluation of the microbiome effects of easy and hard keeper horses with the application of the Equine Keeper Status Scale
JEVS May 2021 Vol 100 Proceedings of the Virtual Equine Science Symposium 1-4 June 2021 103465
Presentation by Alexa Johnson
The horse's unique microbiome contains bacteria, archaea, protozoa and anaerobic fungi, and is responsible for fermenting fibrous feed to volatile fatty acids (VFAs), which it is estimated can provide up to 70% of a horse's energy requirements.
Leng J, McNally S, Walton G, Swann J, Proudman C, Argo C, Emery S, La Ragione R, Eustace R.
Hay vs. haylage; forage type influences the equine urinary metabonome and faecal microbiota.
Equine Vet J. 2021 Apr 26. doi: 10.1111/evj.13456. Epub ahead of print. PMID: 33900659.
Tuniyazi M, He J, Guo J, Li S, Zhang N, Hu Z, Fu Y
Changes of microbial and metabolome of the equine hindgut during oligofructose-induced laminitis
BMC Vet Res 17, 11 (2021). https://doi.org/10.1186/s12917-020-02686-9
Fitzgerald DM, Spence RJ, Stewart ZK, Prentis PJ, Sillence MN, de Laat MA.
The effect of diet change and insulin dysregulation on the faecal microbiome of ponies.
J Exp Biol. 2020 Apr 1;223(Pt 7):jeb219154. doi: 10.1242/jeb.219154. PMID: 32098884.
Keywords: 16S rRNA; Endocrine; Equine metabolic syndrome; Glucagon-like peptide-1; Hindgut; Horse.
Morrison PK, Newbold CJ, Jones E, Worgan HJ, Grove-White DH, Dugdale AH, Barfoot C, Harris PA, Argo CM
The Equine Gastrointestinal Microbiome: Impacts of Age and Obesity
Front Microbiol. 07 Dec 2018 9:3017. doi: 10.3389/fmicb.2018.03017
Biddle AS, Tomb JF, Fan Z.
Microbiome and Blood Analyte Differences Point to Community and Metabolic Signatures in Lean and Obese Horses.
Front Vet Sci. 2018 Sep 20;5:225. doi: 10.3389/fvets.2018.00225. PMID: 30294603; PMCID: PMC6158370.
Keywords: 16S rRNA; equine gut microbiome; glucose; insulin; leptin; network analysis; obesity; triglycerides.
Obese horses had greater phyla diversity and greater richness of gut bacteria than lean horses, and higher blood glucose, cortisol, triglycerides and leptin. Taxa associated with a healthy gut were correlated with obesity: Propionibacteriaceae (a propionate producer), Butyrivibrio species (butyrate producers), Ruminococcaceae (fibre degraders) and Sutterella species. There was no correlation between resting insulin and microbiome taxa abundance.
Salem SE, Maddox TW, Berg A, Antczak P, Ketley JM, Williams JN, Archer DC
Variation in faecal microbiota in a group of horses managed at pasture over a 12-month period
Sci Rep 8, 8510 (2018). https://doi.org/10.1038/s41598-018-26930-3
Studying dung collected every 14 days from 7 healthy horses kept at grass (with supplemental haylage when grass was sparse) showed that the fecal microbiota constantly changed in response to changes in the grass and feeding of haylage and weather conditions over 12 months, and suggested that fluctuation in the microbiota is a normal response to dietary and environmental changes. There was significant difference in faecal microbiota between horses on the same diet of pasture and haylage. Ambient temperature and rainfall affected the faecal microbiota - this could be because of changes in the grass, or the effect of weather on environmental bacteria eaten with the grass (which have been shown to survive enzymatic digestion in the stomach and to colonise the hindgut resulting in shifts in gut microbiota).
The faecal microbiota was dominated by members of the Firmicutes and Bacteroidetes phyla (with Fibrobacteres, Spirochaetes, Verrucomicrobia and Proteobacteria being the other significant bacterial phyla identified). Other studies have found horse faecal microbiota dominated by Firmicutes and Verrucomicrobia phyla, but the sequencing technology used may account for variation in results.
When haylage was fed, the relative abundance of members of the phylum Fibrobacters and Spirochaetes increased, and Firmicutes decreased. Fibrobacteres is effective at hydrolysing plant cellulose.
The research concluded that the equine microbiome is highly dynamic, responds to dietary factors and ambient environmental conditions, changed over 12 months but did not cause any clinical abnormalities.
Salem et al. 2018 Supplementary figure S2 - showing test following worming (red circle) and grass only (no haylage) period (wk 6 8 June to wk 19 23 December) beneath turquoise line.
Elzinga SE, Weese JS, Adams AA
Comparison of the Fecal Microbiota in Horses With Equine Metabolic Syndrome and Metabolically Normal Controls Fed a Similar All-Forage Diet
Journal of Equine Veterinary Science Sept 2016 Volume 44 , 9 - 16
Elzinga found that horses with EMS had lower microbial diversity than healthy horses, and with a greater abundance of Verrucomicrobiota subdivision 5 (now classified as a separate phyla Kiritimatiellaeota). "Equine metabolic syndrome horses exhibited a decrease in fecal microbial diversity, and there were differences in overall community structure between EMS horses and controls."
Fecal Microflora and Dysbosis; Contribution to Metabolic Syndrome, Inflammation and Leaky Gut Syndrome - Tom Schell, Secondvet, May 2015
Dougal K, de la Fuente G, Harris PA, Girdwood SE, Pinloche E, Geor RJ, Nielsen BD, Schott II HC, Elzinga S, Newbold CJ
Characterisation of the Faecal Bacterial Community in Adult and Elderly Horses Fed a High Fibre, High Oil or High Starch Diet Using 454 Pyrosequencing.
PLoS ONE 2014 9(2): e87424. https://doi.org/10.1371/journal.pone.0087424
Conclusions: "...feeding different diets results in significant changes in the faecal bacterial microbiome. Also identified is a reduction in bacterial diversity in older horses. Furthermore we confirm the presence of only a small core bacterial community which is found in all horses regardless of age or diet, composed predominantly of the Lachnospiraceae."
Steelman SM, Chowdhary BP, Dowd S, Suchodolski J, Janečka JE.
Pyrosequencing of 16S rRNA genes in fecal samples reveals high diversity of hindgut microflora in horses and potential links to chronic laminitis.
BMC Vet Res. 2012 Nov 27;8:231. doi: 10.1186/1746-6148-8-231. PMID: 23186268; PMCID: PMC3538718.
Important to note that the horses were not matched for age or breed or location or diet: 10 control horses were all Quarter Horses, 8 laminitis horses were 3 QH, 2 Arabian, 1 WB, 1 pony, 1 TB, ages were mean 7.7 years for control and mean >15 years for laminitis, 9 control & 1 laminitis lived on Farm A, 7 laminitis and 1 control lived on Farm B, all control horses ate a 16% protein pellet, all laminitis horses ate a 12% protein pellet, all horses ate coastal hay (but was it from the same source?), but 6/10 control also ate alfalfa.
Milinovich GJ, Klieve AV, Pollitt CC, Trott DJ
Microbial events in the hindgut during carbohydrate-induced equine laminitis
Vet Clin North Am Equine Pract. 2010 Apr;26(1):79-94. doi: 10.1016/j.cveq.2010.01.007
Comparison of the Fecal Microbiota in Horses With Equine Metabolic Syndrome and Metabolically Normal Controls Fed a Similar All-Forage Diet
Journal of Equine Veterinary Science Sept 2016 Volume 44 , 9 - 16
Elzinga found that horses with EMS had lower microbial diversity than healthy horses, and with a greater abundance of Verrucomicrobiota subdivision 5 (now classified as a separate phyla Kiritimatiellaeota). "Equine metabolic syndrome horses exhibited a decrease in fecal microbial diversity, and there were differences in overall community structure between EMS horses and controls."
Fecal Microflora and Dysbosis; Contribution to Metabolic Syndrome, Inflammation and Leaky Gut Syndrome - Tom Schell, Secondvet, May 2015
Dougal K, de la Fuente G, Harris PA, Girdwood SE, Pinloche E, Geor RJ, Nielsen BD, Schott II HC, Elzinga S, Newbold CJ
Characterisation of the Faecal Bacterial Community in Adult and Elderly Horses Fed a High Fibre, High Oil or High Starch Diet Using 454 Pyrosequencing.
PLoS ONE 2014 9(2): e87424. https://doi.org/10.1371/journal.pone.0087424
Conclusions: "...feeding different diets results in significant changes in the faecal bacterial microbiome. Also identified is a reduction in bacterial diversity in older horses. Furthermore we confirm the presence of only a small core bacterial community which is found in all horses regardless of age or diet, composed predominantly of the Lachnospiraceae."
Steelman SM, Chowdhary BP, Dowd S, Suchodolski J, Janečka JE.
Pyrosequencing of 16S rRNA genes in fecal samples reveals high diversity of hindgut microflora in horses and potential links to chronic laminitis.
BMC Vet Res. 2012 Nov 27;8:231. doi: 10.1186/1746-6148-8-231. PMID: 23186268; PMCID: PMC3538718.
Important to note that the horses were not matched for age or breed or location or diet: 10 control horses were all Quarter Horses, 8 laminitis horses were 3 QH, 2 Arabian, 1 WB, 1 pony, 1 TB, ages were mean 7.7 years for control and mean >15 years for laminitis, 9 control & 1 laminitis lived on Farm A, 7 laminitis and 1 control lived on Farm B, all control horses ate a 16% protein pellet, all laminitis horses ate a 12% protein pellet, all horses ate coastal hay (but was it from the same source?), but 6/10 control also ate alfalfa.
Milinovich GJ, Klieve AV, Pollitt CC, Trott DJ
Microbial events in the hindgut during carbohydrate-induced equine laminitis
Vet Clin North Am Equine Pract. 2010 Apr;26(1):79-94. doi: 10.1016/j.cveq.2010.01.007
Minerals
Minerals play a vital role in keeping horses healthy. Both the amount of minerals available in the diet and the ratios between the minerals are important, as too much or too little of one mineral can change the requirement for another mineral.
To calculate your horse's mineral requirements, use the National Research Council's online programme, based on the Nutrient Requirements of Horses 2007.
NRC Nutrient Requirements of Horses 1989 Minerals p10 onwards
Equine Nutrition and Feeding David Frape 2010 Minerals chapter 3 p37 onwards
For diet suggestions including information about minerals and vitamins, see Diet.
In the UK individual minerals can be purchased from:
Equimins - ask for their Straight Minerals price list. Products may include: brewers yeast, calcium carbonate, L-carnitine, copper sulphate, Bioplex copper proteinate, dicalcium phosphate, lysine, magnesium oxide, monosodium phosphate, sodium selenite, selenium yeast, vitamin E oil, zinc oxide, zinc sulphate. Click here for an example of minerals available from Equimins (NB prices and products available may have changed).
Forageplus www.forageplus.com
Products include:
calcium carbonate 39.4% Ca, bioplex copper 10% Cu, bioplex manganese 15% Mn, bioplex zinc 15% Zn, biotin 2%, L-Lysine 100%, magnesium oxide (heavy grade) 60.7% Mg, monosodium phosphate 24% P, 20% Na, selenium yeast 2mg/g, Vit E oil 500 IU/g, jiaogulan, DL-Methionine 99%.
Progressive Earth www.progressive-earth.com
To calculate your horse's mineral requirements, use the National Research Council's online programme, based on the Nutrient Requirements of Horses 2007.
NRC Nutrient Requirements of Horses 1989 Minerals p10 onwards
Equine Nutrition and Feeding David Frape 2010 Minerals chapter 3 p37 onwards
For diet suggestions including information about minerals and vitamins, see Diet.
In the UK individual minerals can be purchased from:
Equimins - ask for their Straight Minerals price list. Products may include: brewers yeast, calcium carbonate, L-carnitine, copper sulphate, Bioplex copper proteinate, dicalcium phosphate, lysine, magnesium oxide, monosodium phosphate, sodium selenite, selenium yeast, vitamin E oil, zinc oxide, zinc sulphate. Click here for an example of minerals available from Equimins (NB prices and products available may have changed).
Forageplus www.forageplus.com
Products include:
calcium carbonate 39.4% Ca, bioplex copper 10% Cu, bioplex manganese 15% Mn, bioplex zinc 15% Zn, biotin 2%, L-Lysine 100%, magnesium oxide (heavy grade) 60.7% Mg, monosodium phosphate 24% P, 20% Na, selenium yeast 2mg/g, Vit E oil 500 IU/g, jiaogulan, DL-Methionine 99%.
Progressive Earth www.progressive-earth.com
MIRG
IR calculator - enter your horse's glucose and insulin blood results and the G:I ratio, RISQI, MIRG and IR status is calculated for you.
MRI - Magnetic Resonance Imaging
MRI shows both bone and soft tissue and may be particularly useful for detecting subtle changes to the laminae and foot, with the ability to detect laminar separation/stretching before increases in hoof:laminar zone measurements can be seen on radiographs. Until recently MRI was not often used for laminitis cases due to the cost and need for anesthesia, but now that standing MRI can be carried out under sedation, MRI assessment of laminitis cases may become more common. Although literature regarding the use of MRI for laminitis cases is limited, Ilva Drumm (nee Grundmann) et al. 2015 published normal measurements for MRI assessment of laminitis, Arble et al. 2009 described MRI in active laminitis, and Murray et al. 2003 described MRI in chronic laminitis.
Yamada K, Inui T, Itoh M, Yanagawa M, Sato F, Tominari M, Mizobe F, Kishimoto M, Sasaki N
Characteristic findings of magnetic resonance imaging (MRI) and computed tomography (CT) for severe chronic laminitis in a Thoroughbred horse
J. Equine Sci. May 2017 Vol. 28, No. 3 pp. 105–110, 2017
Grundmann IN, Drost WT, Zekas LJ, Belknap JK, Garabed RB, Weisbrode SE, Parks AH, Knopp MV, Maierl J
Quantitative assessment of the equine hoof using digital radiography and magnetic resonance imaging
Equine Vet J. 2015 Sep;47(5):542-7. doi: 10.1111/evj.12340. Epub 2014 Nov 3
based on:
Drumm INM (nee Grundmann)
Quantitative Assessment of the Equine Hoof Using Digital Radiography and Magnetic Resonance Imaging
PhD dissertation 2015 Ludwig Maximilians University Munich
and
Grundmann, Ilva
Digital Radiographic and Magnetic Resonance Imaging of the Normal Equine Foot: a Focus on the Soft Tissue Structures of the Hoof Wall and Sole
MSc thesis 2012 Ohio State University
Identifying Laminitic Changes with MRI - Michelle Anderson, Dec 2012, www.thehorse.com
Magnetic Resonance Imaging in the Horse: an Introduction - Judy Carter ACVS Proceedings 2011(shows axial images of the foot).
Arble JB, Mattoon JS, Drost WT, Weisbrode SE, Wassenaar PA, Pan X, Hunt RJ, Belknap JK
Magnetic resonance imaging of the initial active stage of equine laminitis at 4.7 T
Vet Radiol Ultrasound. 2009 Jan-Feb;50(1):3-12
"Signal intensity and architectural changes within the corium and laminae were readily seen at 4.7 T, and there was a strong association with the histologic diagnosis of active laminitis. Measurements obtained with MR imaging were more sensitive and specific predictors of laminitis than those obtained radiographically. Subjective evaluation with MR imaging was more sensitive than with radiography and should become more specific with greater understanding of normal anatomy."
Murray RC, Dyson SJ, Schramme MC, Branch M, Woods S
Magnetic resonance imaging of the equine digit with chronic laminitis
Vet Radiol Ultrasound. 2003 Nov-Dec;44(6):609-17 (Full paper)
"Features consistently noted with MR images in group L, but not detected using radiography, included laminar disruption, circumscribed areas of laminar gas, laminar fluid, and bone medullary fluid. Other findings seen only on MR images included increased size and number of vascular channels, alterations in the corium coronae, and distal interphalangeal joint distension. Magnetic resonance imaging allowed better definition of laminar gas lines and P3 surface irregularity observed on radiographs. Based on measurements, group L had a greater angle of rotation, distal displacement, and dorsal hoof wall thickness than group N; forelimb hoof wall thickness was greater than hindlimb; and distal displacement and hoof wall thickness measurements were smaller using MR imaging than radiography, but had a similar pattern. It is concluded that there are features of chronic laminitis consistently observed using MR imaging and that these may be additional to features observed radiographically."
Keller MD, Galloway GJ, Pollitt CC
Magnetic resonance microscopy of the equine hoof wall: a study of resolution and potential
Equine Veterinary Journal, 38: 461–466 2006. doi: 10.2746/042516406778400565
"Although MR images with microscopic resolution were obtained ex vivo, this study demonstrates the potential for detection of lamellar pathology as it occurs. Early recognition of the development of laminitis to instigate effective therapy at an earlier stage and may improve the outcome for laminitic horses."
MRI shows both bone and soft tissue and may be particularly useful for detecting subtle changes to the laminae and foot, with the ability to detect laminar separation/stretching before increases in hoof:laminar zone measurements can be seen on radiographs. Until recently MRI was not often used for laminitis cases due to the cost and need for anesthesia, but now that standing MRI can be carried out under sedation, MRI assessment of laminitis cases may become more common. Although literature regarding the use of MRI for laminitis cases is limited, Ilva Drumm (nee Grundmann) et al. 2015 published normal measurements for MRI assessment of laminitis, Arble et al. 2009 described MRI in active laminitis, and Murray et al. 2003 described MRI in chronic laminitis.
Yamada K, Inui T, Itoh M, Yanagawa M, Sato F, Tominari M, Mizobe F, Kishimoto M, Sasaki N
Characteristic findings of magnetic resonance imaging (MRI) and computed tomography (CT) for severe chronic laminitis in a Thoroughbred horse
J. Equine Sci. May 2017 Vol. 28, No. 3 pp. 105–110, 2017
Grundmann IN, Drost WT, Zekas LJ, Belknap JK, Garabed RB, Weisbrode SE, Parks AH, Knopp MV, Maierl J
Quantitative assessment of the equine hoof using digital radiography and magnetic resonance imaging
Equine Vet J. 2015 Sep;47(5):542-7. doi: 10.1111/evj.12340. Epub 2014 Nov 3
based on:
Drumm INM (nee Grundmann)
Quantitative Assessment of the Equine Hoof Using Digital Radiography and Magnetic Resonance Imaging
PhD dissertation 2015 Ludwig Maximilians University Munich
and
Grundmann, Ilva
Digital Radiographic and Magnetic Resonance Imaging of the Normal Equine Foot: a Focus on the Soft Tissue Structures of the Hoof Wall and Sole
MSc thesis 2012 Ohio State University
Identifying Laminitic Changes with MRI - Michelle Anderson, Dec 2012, www.thehorse.com
Magnetic Resonance Imaging in the Horse: an Introduction - Judy Carter ACVS Proceedings 2011(shows axial images of the foot).
Arble JB, Mattoon JS, Drost WT, Weisbrode SE, Wassenaar PA, Pan X, Hunt RJ, Belknap JK
Magnetic resonance imaging of the initial active stage of equine laminitis at 4.7 T
Vet Radiol Ultrasound. 2009 Jan-Feb;50(1):3-12
"Signal intensity and architectural changes within the corium and laminae were readily seen at 4.7 T, and there was a strong association with the histologic diagnosis of active laminitis. Measurements obtained with MR imaging were more sensitive and specific predictors of laminitis than those obtained radiographically. Subjective evaluation with MR imaging was more sensitive than with radiography and should become more specific with greater understanding of normal anatomy."
Murray RC, Dyson SJ, Schramme MC, Branch M, Woods S
Magnetic resonance imaging of the equine digit with chronic laminitis
Vet Radiol Ultrasound. 2003 Nov-Dec;44(6):609-17 (Full paper)
"Features consistently noted with MR images in group L, but not detected using radiography, included laminar disruption, circumscribed areas of laminar gas, laminar fluid, and bone medullary fluid. Other findings seen only on MR images included increased size and number of vascular channels, alterations in the corium coronae, and distal interphalangeal joint distension. Magnetic resonance imaging allowed better definition of laminar gas lines and P3 surface irregularity observed on radiographs. Based on measurements, group L had a greater angle of rotation, distal displacement, and dorsal hoof wall thickness than group N; forelimb hoof wall thickness was greater than hindlimb; and distal displacement and hoof wall thickness measurements were smaller using MR imaging than radiography, but had a similar pattern. It is concluded that there are features of chronic laminitis consistently observed using MR imaging and that these may be additional to features observed radiographically."
Keller MD, Galloway GJ, Pollitt CC
Magnetic resonance microscopy of the equine hoof wall: a study of resolution and potential
Equine Veterinary Journal, 38: 461–466 2006. doi: 10.2746/042516406778400565
"Although MR images with microscopic resolution were obtained ex vivo, this study demonstrates the potential for detection of lamellar pathology as it occurs. Early recognition of the development of laminitis to instigate effective therapy at an earlier stage and may improve the outcome for laminitic horses."
Muscle wasting
Muscle wasting (muscle atrophy, sarcopenia) is a common clinical sign of PPID.
Muscle Loss: Atrophy Scoring System for Horses Introduced - KER January 2022
Banse HE, Whitehead AE, McFarlane D, Chelikani PK
Markers of muscle atrophy and impact of treatment with pergolide in horses with pituitary pars intermedia dysfunction and muscle atrophy
Domestic Animal Endocrinology July 2021 Vol 76. Published online 18 February 2021. doi.org/10.1016/j.domaniend.2021.106620.
Keywords: Proteolysis; Weight loss; Equine; Insulin; Adiposity
Aleman M, Watson JL, Williams DC, LeCouteur RA, Nieto JE, Shelton GD
Myopathy in horses with pituitary pars intermedia dysfunction (Cushing's disease)
Neuromuscul Disord. 2006 Nov;16(11):737-44 (PubMed)
"Similar to other species, this study confirmed atrophy of type 2 fibers as the cause of muscle mass loss in horses with Cushing's disease."
Muscle Loss: Atrophy Scoring System for Horses Introduced - KER January 2022
Banse HE, Whitehead AE, McFarlane D, Chelikani PK
Markers of muscle atrophy and impact of treatment with pergolide in horses with pituitary pars intermedia dysfunction and muscle atrophy
Domestic Animal Endocrinology July 2021 Vol 76. Published online 18 February 2021. doi.org/10.1016/j.domaniend.2021.106620.
Keywords: Proteolysis; Weight loss; Equine; Insulin; Adiposity
Aleman M, Watson JL, Williams DC, LeCouteur RA, Nieto JE, Shelton GD
Myopathy in horses with pituitary pars intermedia dysfunction (Cushing's disease)
Neuromuscul Disord. 2006 Nov;16(11):737-44 (PubMed)
"Similar to other species, this study confirmed atrophy of type 2 fibers as the cause of muscle mass loss in horses with Cushing's disease."
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Muzzles
If your horse is overweight and on a weight loss diet, and/or if he has been diagnosed with EMS/insulin dysregulation but his insulin levels have now returned to or close to normal, you may want him to have some time at grass, but you need to consider how you are going to restrict his grass intake - small paddock or track system, strip grazing, limited access and/or muzzles are the usual options. Using a grazing muzzle reduces the amount of grass that a horse can eat, slowing down a fast/excessive eater and often increasing the horse's amount of exercise. Before using a grazing muzzle, please read the latest advice from the NEWC:
NEWC Grazing Muzzle Guidance and watch their video: NEWC Grazing Muzzle Guidance video |
|
How much does wearing a muzzle restrict grazing?
Research has found that wearing a grazing muzzle can reduce grass intake considerably.
Longland AC, Barfoot C, Harris PA
Efficacy of Wearing Grazing Muzzles for 10 Hours per Day on Controlling Bodyweight in Pastured Ponies
Journal of Equine Veterinary Science Oct 2016, Volume 45 , 22 - 27
Longland AC, Barfoot C, Harris PA
Effects of Grazing Muzzles on Intakes of Dry Matter and Water-Soluble Carbohydrates by Ponies Grazing Spring, Summer, and Autumn Swards, as well as Autumn Swards of Different Heights
Journal of Equine Veterinary Science Volume 40, May 2016, Pages 26-33 (DeepDyve)
Glunk EC, Sheaffer CC, Hathaway MR, Martinson KL
Interaction of Grazing Muzzle Use and Grass Species on Forage Intake of Horses
Journal of Equine Veterinary Science July 2014, Volume 34 , Issue 7 , 930 - 933
Use of a grazing muzzle was thought to reduce grass intake by an average of 30%.
See also:
The interaction of grazing muzzle use and grass species on forage intake of horses - Krishona Martinson, Emily Glunk, Craig Sheaffer and Marcia Hathaway - University of Minnesota
Horses Wearing Muzzles Show Different Grazing Habits - KER staff Sept 2014
A Longland, P Harris, C Barfoot
The effect of wearing a grazing muzzle vs not wearing a grazing muzzle on pasture dry matter intake by ponies
J Equine Veterinary Science 2011 31: 282-283
Use of muzzles: ponies allowed to graze for 3 hours with a muzzle ate an average of 0.14% BW, 83% less than ponies without a muzzle - muzzled ponies did not eat more than 0.5 kg DM compared to unmuzzled ponies who ate around 3.3 kg DM (an average of 0.8% BW).
See also:
Grazing Muzzles Reduce Pasture Consumption by 80 Percent in Grazing Ponies, According to New Study - Fran Jurga The Hoof Blog - 16 June 2011
Grazing Muzzles' Efficacy at Reducing Pasture Intake - Erica Larson Sept 2011 www.thehorse.
A. C. Longland, C. Barfoot, P. A. Harris
The effect of wearing a grazing muzzle vs. not wearing a grazing muzzle on intakes of spring, summer and autumn pastures by ponies
Forages and grazing in horse nutrition Volume 132, 2012, pp 185-186
Ponies were monitored for 3 hours on 4 occasions grazing spring, summer, autumn and winter pastures with and without a muzzle. Wearing a muzzle was estimated to reduce grass intake by between 77 and 83%.
Grazing Muzzles for Horses: How Effective Are They? - Kentucky Equine Research Staff - May 16, 2013
If you aren't convinced about using a muzzle for your EMS/PPID horse, read Linda Cowles' article about muzzles, and see the photo of Nancy, whose owner wouldn't use a muzzle.
See Muzzled for Moderation by Christine Barakat and Melinda Freckleton for a good photo guide of a muzzle that is too small, too big and just right.
Using a grazing muzzle to control grass intake - Tracey Hammond - www.dengie.com
Tracey's tips for using a grazing muzzle:
Research has found that wearing a grazing muzzle can reduce grass intake considerably.
Longland AC, Barfoot C, Harris PA
Efficacy of Wearing Grazing Muzzles for 10 Hours per Day on Controlling Bodyweight in Pastured Ponies
Journal of Equine Veterinary Science Oct 2016, Volume 45 , 22 - 27
Longland AC, Barfoot C, Harris PA
Effects of Grazing Muzzles on Intakes of Dry Matter and Water-Soluble Carbohydrates by Ponies Grazing Spring, Summer, and Autumn Swards, as well as Autumn Swards of Different Heights
Journal of Equine Veterinary Science Volume 40, May 2016, Pages 26-33 (DeepDyve)
Glunk EC, Sheaffer CC, Hathaway MR, Martinson KL
Interaction of Grazing Muzzle Use and Grass Species on Forage Intake of Horses
Journal of Equine Veterinary Science July 2014, Volume 34 , Issue 7 , 930 - 933
Use of a grazing muzzle was thought to reduce grass intake by an average of 30%.
See also:
The interaction of grazing muzzle use and grass species on forage intake of horses - Krishona Martinson, Emily Glunk, Craig Sheaffer and Marcia Hathaway - University of Minnesota
Horses Wearing Muzzles Show Different Grazing Habits - KER staff Sept 2014
A Longland, P Harris, C Barfoot
The effect of wearing a grazing muzzle vs not wearing a grazing muzzle on pasture dry matter intake by ponies
J Equine Veterinary Science 2011 31: 282-283
Use of muzzles: ponies allowed to graze for 3 hours with a muzzle ate an average of 0.14% BW, 83% less than ponies without a muzzle - muzzled ponies did not eat more than 0.5 kg DM compared to unmuzzled ponies who ate around 3.3 kg DM (an average of 0.8% BW).
See also:
Grazing Muzzles Reduce Pasture Consumption by 80 Percent in Grazing Ponies, According to New Study - Fran Jurga The Hoof Blog - 16 June 2011
Grazing Muzzles' Efficacy at Reducing Pasture Intake - Erica Larson Sept 2011 www.thehorse.
A. C. Longland, C. Barfoot, P. A. Harris
The effect of wearing a grazing muzzle vs. not wearing a grazing muzzle on intakes of spring, summer and autumn pastures by ponies
Forages and grazing in horse nutrition Volume 132, 2012, pp 185-186
Ponies were monitored for 3 hours on 4 occasions grazing spring, summer, autumn and winter pastures with and without a muzzle. Wearing a muzzle was estimated to reduce grass intake by between 77 and 83%.
Grazing Muzzles for Horses: How Effective Are They? - Kentucky Equine Research Staff - May 16, 2013
If you aren't convinced about using a muzzle for your EMS/PPID horse, read Linda Cowles' article about muzzles, and see the photo of Nancy, whose owner wouldn't use a muzzle.
See Muzzled for Moderation by Christine Barakat and Melinda Freckleton for a good photo guide of a muzzle that is too small, too big and just right.
Using a grazing muzzle to control grass intake - Tracey Hammond - www.dengie.com
Tracey's tips for using a grazing muzzle:
- Introduce gradually and make wearing a muzzle a positive experience - feed treats or grass through the hole to show your horse that he can eat with the muzzle on. Leave the muzzle on for short periods initially and slowly increase the time spent muzzled.
- Ensure your horse can drink when wearing a muzzle.
- Ensure the muzzle fits correctly.
- Don't leave the muzzle on 24/7 - up to 12 hours is often recommended. Ensure your horse eats at least 1-1.5% of his bodyweight in fibre each day, by supplying high fibre low sugar/starch feeds such as hay or low sugar chaffs (TLS suggests Dengie HiFi molasses free as a chaff hay replacer).
- Remove your horse from grass when not wearing the muzzle to avoid him compensating for the grazing restriction when muzzled.
Homer's muzzle experience
All too often I hear owners say "my horse won't wear a muzzle", "he doesn't like his muzzle", and even "muzzles are cruel", and I understand, because I was almost beaten by what I saw as Homer's refusal to wear a muzzle. But he had recovered from laminitis and rotation, his insulin was in the normal range, and I wanted him to start having some grass and a bit more of a "normal" life.
When I first tried using a muzzle on Homer he would go and stand in his shelter, totally depressed. He then started to run away, in increasing panic, when I approached with the muzzle, and then when I approached with anything that could be a muzzle in my hands, making it difficult to catch him. I spent hours picking bits of grass and holding them up to the hole in the muzzle, trying to persuade him that he could eat grass with it on. We even made the hole slightly bigger. For months I tried sporadically to get him to wear the muzzle, then gave up because he clearly hated it. But this meant he was spending hours in a small mostly mud paddock, eating hay, away from his friends, and moving very little.
Then something I read made me realize that my attitude was wrong. I had to make the muzzle something Homer would love, and choose to wear. I started to feed him handfuls of his feed or grass in the muzzle, not putting the muzzle on but just holding it up for him to reach into, until he started to come towards me when he saw me approach with the muzzle because he knew something tasty was coming. Then I fastened it for a minute or two at a time, slowly increasing the time, still offering him something nice to eat. Then I made it a rule that he could only go out into the big field with his mates when he was wearing his muzzle - no muzzle, no grass.
When I first tried using a muzzle on Homer he would go and stand in his shelter, totally depressed. He then started to run away, in increasing panic, when I approached with the muzzle, and then when I approached with anything that could be a muzzle in my hands, making it difficult to catch him. I spent hours picking bits of grass and holding them up to the hole in the muzzle, trying to persuade him that he could eat grass with it on. We even made the hole slightly bigger. For months I tried sporadically to get him to wear the muzzle, then gave up because he clearly hated it. But this meant he was spending hours in a small mostly mud paddock, eating hay, away from his friends, and moving very little.
Then something I read made me realize that my attitude was wrong. I had to make the muzzle something Homer would love, and choose to wear. I started to feed him handfuls of his feed or grass in the muzzle, not putting the muzzle on but just holding it up for him to reach into, until he started to come towards me when he saw me approach with the muzzle because he knew something tasty was coming. Then I fastened it for a minute or two at a time, slowly increasing the time, still offering him something nice to eat. Then I made it a rule that he could only go out into the big field with his mates when he was wearing his muzzle - no muzzle, no grass.
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That worked well for a while, but then he learned to get the muzzle off by rolling and dragging it over his ears with his front legs (a Shires muzzle with a velcro-fastening headpiece (above). So it was adapted slightly and fitted to a leather headcollar (right), and he was only turned out onto grass when we were around to keep an eye on him. He soon learned that he couldn't get it off, and he stopped trying.
It wasn't long before he asked to have his muzzle put on, as he always got a small treat in it, even if just a handful of the grass he was about to eat, and the other horses appeared to be jealous that Homer was getting something special. Depending on the time of year and the likely sugar content of the grass, he spent part of the day moving around a few acres with his herd, interacting and having the odd gallop, and part of the day in his bare paddock with hay and no muzzle, and his scratching partner would often join him for a while to have a good mutual scratch. He was so much happier, and if anything he lost weight and became fitter with increased, but restricted, access to grass. Homer's access to grass was dependent on his insulin results being well within normal ranges. He was exercised most days and his access to grass reduced on days he didn't exercise. Initially he had access to grass on a track system which was mostly under trees, just first thing in the morning and last thing at night, and as he showed no further signs of laminitis, his insulin remained normal when tested after eating grass, and his exercise returned to pre-laminitis levels, the time he spent grazing was increased and he was able to join his herd in the field until he was out with them most of the time. Eventually his insulin resistance was so well controlled that he was able to graze freely with no muzzle for much of each day. The Best Friend Standard Grazing Muzzle is similar to Homer's "escape free" muzzle - 4 velcro straps attach the muzzle to the horse's own headcollar. |
Attaching a standard muzzle to a leather headcollar with 3 leather straps stopped Homer removing it!
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Muzzle suppliers/manufacturers:
BUYING FROM RETAILERS SIGNED UP TO EASY FUNDRAISING RAISES FUNDS TO SUPPORT THE WORK OF THE LAMINITIS SITE AT NO COST TO YOU - see Easy Fundraising.
ThinLine Flexible Filly grazing muzzle (buying through Equus raises funds for The Laminitis Site at no cost to you - see Easy Fundraising).
JHL Comfort grazing muzzle (buying through VioVet raises funds for The Laminitis Site at no cost to you - see Easy Fundraising).
Best Friend muzzles
see also www.grazingmuzzles.co.uk
Shires comfort grazing muzzle (buying through Oakfield raises funds for The Laminitis Site at no cost to you - see Easy Fundraising).
Shires deluxe comfort grazing muzzle (buying through Viovet raises funds for The Laminitis Site at no cost to you - see Easy Fundraising).
Shires GreenGuard muzzle (buying through Equus raises funds for The Laminitis Site at no cost to you - see Easy Fundraising).
Dinky classic grazing muzzle
Cashel Grazing Muzzle Halter (USA)
BUYING FROM RETAILERS SIGNED UP TO EASY FUNDRAISING RAISES FUNDS TO SUPPORT THE WORK OF THE LAMINITIS SITE AT NO COST TO YOU - see Easy Fundraising.
ThinLine Flexible Filly grazing muzzle (buying through Equus raises funds for The Laminitis Site at no cost to you - see Easy Fundraising).
JHL Comfort grazing muzzle (buying through VioVet raises funds for The Laminitis Site at no cost to you - see Easy Fundraising).
Best Friend muzzles
see also www.grazingmuzzles.co.uk
Shires comfort grazing muzzle (buying through Oakfield raises funds for The Laminitis Site at no cost to you - see Easy Fundraising).
Shires deluxe comfort grazing muzzle (buying through Viovet raises funds for The Laminitis Site at no cost to you - see Easy Fundraising).
Shires GreenGuard muzzle (buying through Equus raises funds for The Laminitis Site at no cost to you - see Easy Fundraising).
Dinky classic grazing muzzle
Cashel Grazing Muzzle Halter (USA)
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In 2023 Dr David Marlin carried out a survey of owners' experiences of grazing muzzles - the results can be read here.
Please note that although some owners reported using a muzzle for 24/24 hours, current recommendations are that a muzzle should not be used for more than 12 hours in 24. From the NEWC Grazing Muzzle Guidance 2015:
"A horse should never be left with a grazing muzzle on 24/7. Academic opinion currently does not recommend use for over 10 to 12 hours per day. Remember that compensatory eating means that time without the muzzle needs to be in a form of restricted grazing/forage provision to ensure all your hard work is not undone. Other methods of prolonging chewing time may be needed to be put in place."
In order of preference, the muzzles most highly recommended by owners were:
1. ThinLine Flexible Filly grazing muzzle (buying through Equus raises funds for The Laminitis Site at no cost to you - see Easy Fundraising).
2. Best Friend Deluxe Grazing Muzzle
3. Ultimate Grazing Muzzle
4. Best Friend Have A Heart Horse Grazing/Laminitis Muzzle
5. CG Equine GreenGuard (sold in the UK as Shires GreenGuard) (buying through VioVet raises funds for The Laminitis Site at no cost to you - see Easy Fundraising).
6. Dinky Classic Grazing Muzzle
Please note that although some owners reported using a muzzle for 24/24 hours, current recommendations are that a muzzle should not be used for more than 12 hours in 24. From the NEWC Grazing Muzzle Guidance 2015:
"A horse should never be left with a grazing muzzle on 24/7. Academic opinion currently does not recommend use for over 10 to 12 hours per day. Remember that compensatory eating means that time without the muzzle needs to be in a form of restricted grazing/forage provision to ensure all your hard work is not undone. Other methods of prolonging chewing time may be needed to be put in place."
In order of preference, the muzzles most highly recommended by owners were:
1. ThinLine Flexible Filly grazing muzzle (buying through Equus raises funds for The Laminitis Site at no cost to you - see Easy Fundraising).
2. Best Friend Deluxe Grazing Muzzle
3. Ultimate Grazing Muzzle
4. Best Friend Have A Heart Horse Grazing/Laminitis Muzzle
5. CG Equine GreenGuard (sold in the UK as Shires GreenGuard) (buying through VioVet raises funds for The Laminitis Site at no cost to you - see Easy Fundraising).
6. Dinky Classic Grazing Muzzle